Whoopie pies are cute as can be and make a wonderful few-bite dessert. You know what makes them even better? Filling them with my favorite (rich, smooth, beloved) vanilla pastry cream. There isn’t much I can resist when this pastry cream is involved and these sweet little treats are no exception. I first saw the idea for Boston cream whoopie pies on a blog ages ago. While the picture looked appealing, the recipe was a somewhat odd vegan version that called for all sorts of ingredients I don’t keep on hand and didn’t sound as good as they looked. I have been hemming and hawing over the idea ever since, trying to think of the best way to accomplish these when wouldn’t you know, a different version popped up in another blog and took care of it for me. Problem solved! A vanilla cake cookie topped with ganache and filled with pastry cream – perfect.
These are just as easy as any other whoopie pie, though it is best to make the pastry cream one day in advance so everything will be ready to assemble once the cookies are baked. One of my favorite things about this recipe? You’ll have left over pastry cream for…you know, eating with a spoon. (Shhh, don’t tell.)
Boston Cream Whoopie Pies
For the pastry cream:
2 cups half-and-half
½ cup sugar, divided
5 large egg yolks
3 tbsp. cornstarch
4 tbsp. cold unsalted butter, cut into 4 pieces
1½ tsp. vanilla extract
Yield: about 32 sandwich cookies
For the cookies:
8 tbsp. unsalted butter, at room temperature
¾ cup sugar
2 tsp. vanilla extract
2 large eggs
2¼ cups all-purpose flour
1½ tsp. baking powder
¾ tsp. salt
½ cup milk
For the ganache:
2 oz. bittersweet chocolate, finely chopped
¼ cup heavy cream
To make the pastry cream, heat the half-and-half, 6 tablespoons of the sugar, and the salt in a saucepan over medium-high heat until simmering, stirring occasionally to dissolve the sugar. Meanwhile, combine the egg yolks and remaining 2 tablespoons sugar in a medium bowl and whisk until the sugar has begun to dissolve and the mixture is creamy, about 15 seconds. Whisk in the cornstarch until combined and the mixture is pale yellow and thick, about 30 seconds.
When the half-and-half mixture has reached a simmer, slowly add it to the egg yolk mixture to temper, whisking constantly. Return the mixture to the saucepan, scraping the bowl with a rubber spatula. Return the mixture to a simmer over medium heat, whisking constantly, until a few bubbles burst on the surface and the mixture is thickened and glossy, about 30 seconds. Off the heat, whisk in the butter and vanilla. Strain the pastry cream through a fine mesh sieve set over a medium bowl. Press plastic wrap directly on the surface to prevent a skin from forming and refrigerate until cold and set, at least 3 hours and up to 2 days.
To make the cookies, preheat the oven to 375˚ F. Line two baking sheets with parchment paper or silicone baking mats. Fit a pastry bag with a wide round tip (I used Ateco 809). Combine the butter and sugar in the bowl of an electric mixer and beat on medium-high speed until light and fluffy, about 2 minutes. Blend in the eggs one at a time, beating well after each addition. Blend in the vanilla. In a medium bowl combine the flour, baking powder, and salt; whisk to combine. With the mixer on low speed, add the dry ingredients to the bowl, alternating with with the milk, and beating each addition just until incorporated.
Transfer the batter to the piping bag. Pipe 1½-2 inch circles onto the prepared baking sheets, spacing an inch or two apart. Bake 8-10 minutes, until the cookies are set (they should not brown.) Transfer to a wire rack to cool completely. Repeat with any remaining batter as necessary.
Once all the cookies have cooled, match them up in pairs by size. To make the ganache, place the chopped chocolate into a small heatproof bowl. Bring the heavy cream to a simmer in a small saucepan. Pour the cream over the chocolate and let sit for 1-2 minutes. Whisk in small circular motions until the chocolate is completely blended and the ganache is smooth. Dip the rounded side of one cookie of each pair into the ganache and coat with an even layer. Return to the cooling rack, flat side down, and let the ganache set before proceeding.
Transfer the pastry cream another piping bag fitted with a smaller plain round tip. Pipe a dollop of pastry cream onto the flat side of the plain cookie of each pair. Press the flat side of the other cookie to the pastry cream, sandwiching the two together.
Keep refrigerated in an airtight container for up to 2 days.