Surprise Cookies

1 3/4 cups all-purpose flour
3/4 cup cocoa powder
1/2 tsp. baking soda
1/2 tsp. salt
1/2 cup (1 stick) unsalted butter, softened
1 cup sugar
1 large egg
1/2 cup milk
1 tsp. pure vanilla extract
12 large marshmallows, cut in half horizontally (could use marshmallow stackers)

Preheat oven to 375.  In a medium bowl, whisk together flour, cocoa powder, baking soda, and salt; set aside.

In a 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 begin 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.

Chocolate Frosting
2 cups powdered sugar
4 tbsp. (1/2 stick) unsalted butter, melted and cooled
1/4 cup cocoa powder
1/4 cup milk
1/4 tsp. vanilla extract

Place powdered sugar in a medium bowl.  Whisk in butter and cocoa powder.  Ad milk and vanilla, and whisk until well combined.