I am having trouble with a buttercream recipe from sew sweet. It is a faux fondant type. No matter what I do it bulges out the sides of the cake layers. Even if I crumb coat and let sit overnight. My cakes are from scratch so they are heavier. recipe is: 2 cups crisco, 4lbs. powdered sugar, 1/2 cup corn starch, 1 cup water, 1/2 tsp of each of the following flavors: clear vanilla, creme bouquet, coconut, almond and butter.
Hi and Welcome to CC, 1bubbles1.
The problem might not be with your recipe, it's necessary to allow your cake to "rest" after filling in order to allow it to settle (to prevent just what you're describing):