Nothing says "Boston" quite like a Boston cream pie. For the uninitiated, the official dessert of Massachusetts is not a pie at all, but rather slices of vanilla sponge cake soaked in a mocha syrup, layered with pastry cream, and smothered in a bittersweet chocolate ganache. Sound enticing? We think so, too. That's why we're hunkering down this weekend and whipping up James Beard Award winner Joanne Chang's recipe from her popular Beantown-based bakery Flour, featured in her sophomore cookbook, appropriately named Flour, Too ($26; amazon.com). By using a combination of pastry and whipped cream in lieu of the traditional heavy crème pâtissière, she achieves a perfectly light and airy taste that'll have you begging for seconds ... and thirds. Read on for the full how-to.
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Best Boston Cream Pie
Serves 4 to 6
4 large eggs, separated, plus 3 egg whites
1 cup granulated sugar
2 tbsp freshly squeezed lemon juice
3/4 cup all-purpose flour
Pinch of kosher salt
Pastry Cream (yields 1 3/4 cup)
1 1/4 cups milk
1/2 cup granulated flour
1/4 cup cake flour
1/2 kosher salt
4 egg yolks
1 tsp vanilla extract
Ganache (yields 1 cup)
3/4 cup semisweet or bittersweet chocolate chips, or 4 oz semisweet or bittersweet chocolate, chopped
1/2 cup heavy cream
1/3 cup hot brewed coffee
1/3 cup granulated sugar
1 cup heavy cream
1 3/4 cups Pastry Cream
1 cup ganache, warmed
13-by-18-in rimmed baking sheet
Stand mixer with whisk attachment or handheld mixer
Sifter or sieve
To make the pastry cream
1. In a medium saucepan, heat the milk over medium-high heat until scalded; that is, until small bubbles form along the sides of the pan. While the milk is heating, in a small bowl, stir together the sugar, flour, and salt. (Mixing the flour with the sugar will prevent the flour from clumping when you add it to the egg yolks.) In a medium bowl, whisk the egg yolks until blended, then slowly whisk in the flour mixture. The mixture will be thick and pasty.
2. Remove the milk from the heat and slowly add it to the egg-flour mixture, a little at a time, while whisking constantly. When all of the milk has been incorporated, return the contents of the bowl to the saucepan and heat over medium heat, whisk continuously and vigorously, for about 3 minutes, or until the mixture thickens and comes to a boil. At first, the mixture will be very frothy and liquid; as it cooks longer, it will slowly start to thicken until the frothy bubbles disappear and it becomes more viscous. Once it thickens, stop whisking every few seconds to see if the mixture has come to a boil. If it has not, keep whisking vigorously. As soon as you see it bubbling, immediately go back to whisking for just 10 seconds, and then remove the pan from the heat. Boiling the mixture will thicken it and cook out the flour taste, but if you let it boil for longer than 10 seconds, the mixture can become grainy.
3. Pour, push, and scrape the mixture through the sieve into a small, heatproof bowl. Stir in the vanilla and then cover with plastic wrap, placing it directly on the surface of the cream to prevent a skin from forming. Refrigerate for at least 4 hours, or until cold, before using. The cream can be stored for up to 3 days in an airtight container in the refrigerator.
To make the ganache:
1. Place the chocolate in a small, heatproof bowl. In a small saucepan, heat the cream over high heat until scalded; that is, until small bubbles form along the sides of the pan. Pour the hot cream over the chocolate and let sit for 30 seconds. Slowly whisk the chocolate and cream together until the chocolate is completely melted and the mixture is smooth.
2. Let cool to room temperature. The ganache can be stored in an airtight container in the refrigerator for up to 1 week.
To make the sponge cake:
1. Preheat the oven to 350°F, and place a rack in the middle of the oven. Line the baking sheet with parchment paper.
2. Using the stand mixer or the handheld mixer and a medium bowl, beat together the egg yolks, 1⁄4 cup of the sugar, and the lemon juice on high speed for at least 6 to 8 minutes if using the stand mixer or 10 to 12 minutes if using the handheld mixer, or until thick and doubled in volume. Stop the mixer once or twice and scrape down the sides of the bowl and the whisk to ensure the sugar and yolks are evenly mixed. Transfer to a large bowl and set aside.
3. Clean the bowl and the whisk attachment or beaters (they must be spotlessly clean) and beat the egg whites on medium speed for 2 to 3 minutes with the stand mixer or 4 to 6 minutes with the handheld mixer, or until soft peaks form. The whites will start to froth and turn into bubbles, and eventually the yellowy viscous part will disappear. Keep beating until you can see the tines of the whisk or beaters leaving a slight trail in the whites. To test for the soft-peak stage, stop the mixer and lift the whisk or beaters out of the whites; the whites should peak and then droop. With the mixer on medium speed, add the remaining 3⁄4 cup sugar very slowly, a spoonful or so at a time, taking about 1 minute to add all of the sugar. Continue beating on medium speed for 2 to 3 minutes longer, or until the whites are glossy and shiny and hold a stiff peak when you slowly lift the whisk or beaters straight up and out of the whites.
4. Using a rubber spatula, gently fold about one-third of the whipped whites into the yolk mixture to lighten it. Then gently fold in the remaining egg whites. Sift the flour and salt together over the top of the mixture and fold in gently until the flour is completely incorporated. Pour the batter into the prepared baking sheet.
5. Using the offset spatula, carefully spread the batter evenly to cover the entire baking sheet. Concentrate on spreading the batter toward the corners and edges of the pan. The center will be easier to fill once the edges are filled with batter. Don’t worry about the top being perfectly smooth; it is more important that the batter be spread evenly so that the cake is the same thickness throughout. Bake the cake, rotating the baking sheet back to front about halfway through the baking, for 18 to 24 minutes, or until the top is pale golden brown and springs back when pressed in the center with your fingertips and the cake doesn’t stick to your fingers. Let the cake cool in the pan on the wire rack for about 5 minutes.
6. Line a large cutting board with parchment. Run a paring knife around the edge of the still-warm cake to release it from the sides of the baking sheet, and invert the cake onto the parchment. Carefully peel off the parchment and allow the cake to cool completely. Using a chef’s knife, cut the cake in half crosswise and then in half lengthwise. You should now have four cake layers each about 5 1⁄2-by-8 in. Cut the cardboard so that its dimensions are just slightly larger than the cake layer dimensions.
To make the soaking syrup
In a small bowl, stir together the coffee and sugar until the sugar has dissolved.
1. Using the pastry brush, brush the top of all four cake rectangles evenly with the soaking syrup, using up all of the syrup.
1. Place one cake layer, syrup-side up, on the prepared cardboard rectangle. In a medium bowl, using a mixer or a whisk, whip the heavy cream until it holds very firm, stiff peaks. Fold in the pastry cream until well combined. Using the offset spatula, spread about one-third of the cream mixture over the cake layer. There is a tendency for the cream to mound in the center, so be sure to spread the cream out to the edges of the cake. In fact, to make the best-looking cake possible, it is better if the cream layer is slightly thicker along the edge than in the center.
2. Place a second cake layer, syrup-side up, on top of the cream layer and press down gently so the cake layer is level. Using the offset spatula, spread about half of the remaining cream mixture over the cake layer. Again, you want to spread the cream a bit thicker along the edge of the rectangle to prevent the final cake from doming.
3. Place a third cake layer, syrup-side up, on top of the cream and press down slightly to level the cake. Using the offset spatula, spread the remaining cream mixture over the cake, again making it a bit thicker along the edges than in the center. Top the cake with the final cake layer, syrup-side up, and press down gently so that the top layer is flat. Lightly wrap the cake with plastic wrap, place in the freezer, and freeze for about 8 hours or up to overnight, or until it is frozen solid. (At this point, the cake can instead be put into the freezer just until it has firmed up and then it can be well wrapped and frozen for up to 2 weeks.)
4. At least 3 hours in advance of serving, remove the cake from the freezer and place it on a cutting board. Using a chef’s knife dipped in very hot water, trim the edges of the cake so that they are neat and even. (These trimmings make for great snacking.) Dip and wipe the knife clean several times as you trim to make sure you get a neat, sharp edge on the cake. Trim the cardboard underneath so it is flush with the cake.
5. Place the cake on its cardboard base on a cooling rack set on a baking sheet. Pour the warm ganache over the top of the cake. Using the offset spatula, spread the ganache in an even layer. It will begin to firm up right away when it hits the cold cake, so work quickly to even the surface. Let the excess ganache drip down the sides of the cake, leaving some parts of the cake exposed. Let the ganache set for several seconds, then transfer the cake to a serving plate. Let the cake thaw at room temperature before serving.
From Flour, Too by Joanne Chang, photographs by Michael Harlan Turkell (Chronicle Books, 2013)
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