The cake I am making today will be 3 tier. My son is requesting peanut butter frosting and filling for one of the tiers. My question is: I have only used straight buttercream under fondant, this icing has, butter, peanut butter, powder sugar, vanilla and heavy cream. Will this work under the fondant?
Can the cake stay out and not be in the refrigerator tonight with the heavy cream in the frosting?

The small amount of cream in the recipe will be preserved by the sugar...no need to refrigerate.