Place rack in center of oven and preheat to 350 degrees Fahrenheit.
Lightly mist a 12-cup bundt pan with vegetable oil spray, then dust with flour. Shake out excess flour and set pan aside.
Place cake mix, melted ice cream, eggs and coffee powder in large mixing bowl.
Blend with electric mixer on low speed for 1 minute. Stop machine and scrape down sides of bowl with rubber spatula. Increase mixer speed to medium and beat 2-3 minutes more, scraping down sides again if necessary. The batter should look thick and well-combined.
Pour batter into prepared pan, smoothing it out with rubber spatula.
Bake cake until it springs back when lightly pressed with your finger and is just starting to pull away from the sides of the pan, 40-45 minutes.
Remove pan from oven and place on wire rack to cool for 20 minutes.
Run a long, sharp knife around edge of cake and invert it onto rack to cool completely, 20 minutes more.
Meanwhile as the cake cools, prepare the Chocolate Marshmallow Frosting: Sift confectioner's sugar and cocoa powder together into a large mixing bowl. Set bowl aside.Place marshmallow creme, butter and milk in a medium-size heavy saucepan over medium-low heat. Stir until the butter and marshmallow creme have melted, 2-3 minutes. Remove the pan from the heat. Pour the sugar cocoa mixture over the marshmallow mixture. Add 1 tsp vanilla and stir until frosting is smooth and satiny. Makes 1 1/2 cups.
When the cake is completely cooled, slide the cake onto a serving platter, and pour the warm frosting over the cake. Let the cake rest for 10 minutes before slicing.