Boston Cream Pie Cookies

For Custard: Place 1/2 cup plus 2 tablespoons of the milk, the cream, and the sugar in a medium saucepan over medium heat. Bring just to a boil.

Dissolve the cornstarch and salt in the remaining milk in a small bowl. Whisk in the egg yolk and then whisk into the hot-cream mixture. Whisk over medium-low heat until thick, about 2 to 3 minutes. Remove from the heat and stir in the vanilla.

Transfer to a bowl, cover the surface with plastic wrap, and refrigerate for 2 to 3 hours.

For Cookies: Preheat the oven to 400 degrees F. Lightly spray several baking sheets with nonstick cooking spray. Whisk together the flours, baking soda, and salt in a small bowl.

In a medium bowl, beat the butter, sugar, vanilla, and lemon zest until light and fluffy, about 2 minutes. Beat in the egg yolks and then the whole egg, followed by the buttermilk. Fold in the flour mixture and stir until smooth.

Drop by generous tablespoons about 2 inches apart on the prepared sheets. Bake for 10 to 11 minutes, or until the cookies are firm yet spongy to the touch. Let cool.

Turn a cooled cookie upside down and spread with a rounded tablespoon of cooled custard. Top with a cookie. Continue in this manner until there are no more cookies.

For Chocolate Glaze: Scald the cream in a small saucepan. Transfer to a small bowl and add the chocolate and butter. Whisk until smooth. Add the confectioners' sugar and stir until velvety.

Spread a scant tablespoon of chocolate evenly across the top of each custard-filled cookie. Serve at room temperature.