Makes about 2 dozen
1 3/4 cups all-purpose flour
3/4 cup cocoa powder
1/2 teaspoon baking soda
1/2 teaspoon salt
1/2 cup (1 stick) unsalted butter, softened
1 cup sugar
1 large egg
1/2 cup milk
1 teaspoon pure vanilla extract
12 large marshmallows, cut in half horizontally
Preheat oven to 375 degrees. In a medium bowl, whisk together flour, cocoa powder, baking soda, and salt; set aside.
In the bowl of an electric mixer fitted with the paddle attachment, cream together butter and sugar until light and fluffy, about 2 minutes. Add egg, milk, and vanilla, and beat until well combined. Add reserved flour mixture; mix on low speed until combined.
Using a tablespoon or 1 3/4-inch ice cream scoop, drop dough onto ungreased baking sheets, about 2 inches apart. Bake until cookies begin to spread and become firm, 10 to 12 minutes.
Remove baking sheets from oven, and place a marshmallow, cut-side down, in the center of each cookie, pressing down slightly. Return to oven, and continue baking until marshmallows begins to melt, 2 to 2 1/2 minutes. Transfer cookies to a wire rack to cool completely before frosting.
Spread about 1 tablespoon of frosting over each marshmallow, starting in the center and continuing outward until marshmallow is covered.
FROSTING
Makes 1 cup
2 cups confectioners' sugar
4 tablespoons (1/2 stick) unsalted butter, melted and cooled
1/4 cup cocoa powder
1/4 cup milk
1/4 teaspoon pure vanilla extract
Place confectioners' sugar in a medium bowl. Whisk in butter and cocoa powder. Add milk and vanilla, and whisk until well combined.