Makes 8 pies

FOR THE CAKES
2 cups all-purpose flour
½ cup Dutch-process cocoa powder
1 ¼ teaspoons baking soda
1 teaspoon kosher salt
1 cup buttermilk
1 teaspoon pure vanilla extract
½ cup unsalted butter, softened
1 cup light brown sugar, packed
1 egg

FOR THE FILLING
1 cup (2 sticks) unsalted butter, room temperature
2 cups sifted confectioners' sugar
1 jar (7 1/2 ounces) marshmallow Fluff
2 teaspoons pure vanilla extract

Preheat the oven to 350 degrees.

Line 2 sheet pans with parchment paper.

In a small bowl, whisk together the flour, cocoa, baking soda, and salt.  In another small bowl, stir together buttermilk and vanilla.

In the bowl of a free standing mixer, fitted with a paddle attachment, cream together the butter and brown sugar until light and fluffy, about 3 minutes.  Add the vanilla and egg, scraping down the sides of the bowl to combine. Reduce mixer speed to low and alternately mix in dry ingredients and buttermilk, beginning and ending with dry ingredients.  Scrape down the sides of bowl occasionally, and mix until smooth.

Using a ¼-cup ice cream scoop, drop mounds of batter about 2 inches apart on prepared sheet pans. Bake until tops are puffed, slightly cracked and cakes spring back when lightly touched, 12 to 13 minutes. Transfer cakes to a wire rack to cool completely.

To make the filling, cream together the butter and confectioners’ sugar until light and fluffy, about 3 minutes.  Add vanilla and marshmallow cream, continue beating until smooth and light, about 2 more minutes.

To assemble the pies, dollop a rounded mound of filling on flat sides of half of cakes and top with remaining cakes.