Prepare:
As soon as the cake comes out of the oven, cover the top evenly with:
Sprinkle the marshmallows with:
Return the cake to the oven until the marshmallows soften and puff, 2 to 3 minutes. Remove from the oven and spread over the top:
Spread the frosting gently so as not to dislodge the marshmallows and nuts. Cool the cake in the pan on a rack until the topping is set.