How to Make It
Prepare the dough: Beat butter and sugar with a heavy-duty electric stand mixer on medium-high speed until light and fluffy, about 3 minutes. Add eggs and vanilla. Beat on medium until combined. Melt chocolate chips according to package directions, and cool. Add to butter-sugar mixture; beat on low until blended, stopping to scrape down sides of bowl as needed.
Stir together flour, cocoa, baking powder, 1 teaspoon ground cinnamon, salt, and 1/4 cayenne pepper in a medium bowl. With mixer running on low speed, add flour mixture to butter mixture, beating until just incorporated.
Cover dough; chill 1 hour. Meanwhile, cut 12 large marshmallows in half.
Prepare the cookies: Preheat oven to 350°F. Using a 1 3/4 -inch scoop, drop dough 2 inches apart onto 2 parchment paper-lined baking sheets. Roll each into a ball; flatten to a 1/2-inch thickness. Bake in preheated oven until cookies are almost set, about 8 minutes.
Increase heat to high broil, with oven rack 4 inches from heat. Top each cookie with 1 marshmallow half, cut side down. Broil until marshmallows are lightly browned, 1 to 2 minutes. Cool cookies on baking sheets 2 minutes. Transfer cookies to a wire rack. Sprinkle cookies evenly with remaining 1/8 teaspoon ground cinnamon and a pinch of cayenne pepper. Serve warm, or cool completely.