hot cocoa cookies with marshmallows

the goods:

1/2 cup unsalted butter
1 bag (12 ounces) semisweet chocolate chips
1 and 1/4 cups light brown sugar
3 eggs
2 teaspoons vanilla extract
1/4 cup unsweetened cocoa powder
1 and 1/2 cups all-purpose flour
1 and 1/2 teaspoons baking powder
1/4 teaspoon salt
8 ounces semi-sweet baking chocolate cut into 1-inch pieces
16 large marshmallows, cut in half

In a small saucepan set over medium heat, melt butter and chocolate chips. Stir constantly until just melted. Remove from heat and let cool slightly.
In a large bowl, combine the brown sugar, eggs, and vanilla. Beat with a hand-mixer on medium speed until blended. Beat in the cooled chocolate mixture until combined. Add the cocoa powder, flour, baking powder, and salt. Mix on low speed until just combined. Cover bowl with plastic wrap and refrigerate for 2 hours.
Preheat oven to 325 degrees. Line a cookie sheet with parchment paper. Scoop and drop the cookie dough by the tablespoon onto the prepared sheet 2-inches apart. Bake for 10 minutes, remove from oven and place one piece of chocolate on the center top of each cookie, and then top each chocolate with half of a marshmallow. Place cookies back in the oven for an additional 4 minutes. Remove pan from oven and allow cookies to cool for 5 minutes before transferring to a rack to cool completely. Repeat with remaining dough. Dust with cocoa powder if desired.