Preheat oven to 350 degrees (175 C.) and place the rack in the center of oven.

Lightly mist a 12 cup Bundt pan with vegetable oil spray, then dust with flour.

Shake out excess flour and set the pan aside.

In a large mixing bowl, combine the white cake mix, melted ice cream, and eggs.

Blend with an electric mixer at low speed for 1 minute.

Stop the machine and scrape down the sides of the bowl with a rubber spatula.

Increase the mixer speed to medium and beat for 2 minutes more, scraping down sides if needed.

Ensure the batter is thick and well blended.

Pour the batter into the prepared pan, smoothing the top with a spatula.

Place the cake in the oven.

Bake the cake until it springs back when lightly pressed and just starts to pull away from the sides of the pan, about 38 to 42 minutes.

Remove the pan from the oven and place on a wire rack to cool for 20 minutes.

Remove the cake from the pan.

Meanwhile, prepare the frosting.

Sift the confectioner's sugar and cocoa together in a large mixing bowl.

Set aside.

Place the marshmallows, butter, and milk in a medium heavy saucepan over low heat.

Stir until the marshmallows are melted, about 3 to 4 minutes.

Remove the pan from the heat.

Pour the sugar/cocoa mixture over the marshmallow mixture.

Add the vanilla and stir until the frosting is smooth and satiny.

Place the cake on a serving platter and frost the top and sides.