Marshmallow Whoopie Pies

Makes 20 pies

½ cup unsalted butter
2/3 cups semisweet chocolate chips
2 oz unsweetened chocolate, chopped
1 cup sugar
3 eggs
1 tsp vanilla extract
1 cup flour
¼ cup cocoa powder
½ tsp baking powder
¾ tsp salt
½ tsp instant espresso powder
20 large marshmallows

Preheat oven to 375°F. Place butter and both chocolates in a medium microwave-safe bowl. Microwave at 75 percent power until softened, about 2 minutes. Stir until smooth (microwave for one more minute if needed, to melt completely). Stir in sugar, eggs, and vanilla.

In a separate bowl, whisk together the flour, cocoa powder, baking powder, salt, and espresso powder. Using a spatula, fold dry ingredients into wet ingredients just until mixed. Be careful not to overmix.

Drop heaping tablespoons of batter about 1 inch apart onto a parchment-lined baking sheet. Bake in the preheated 375°F oven about 8 minutes, or until the cookies spring back lightly when touched. Cool for 2-3 minutes.

Transfer half the cookies to a cooling rack, and flip the remaining cookies over, so the flat side is up. Top each cookie with a marshmallow, then place back in the oven for 3 minutes to soften the marshmallows. Remove baking sheet from oven and immediately top with another cookie. Cool completely.