Buttercream frosting is created primarily using butter and sugar. A delicious confection, it stores well either in the refrigerator or freezer but becomes hardened after being chilled or frozen. Re-softening buttercream frosting, however, is simple and will not change the taste or texture.
Allow frozen buttercream frosting to thaw in the refrigerator overnight. Test it with a butter knife, which should slide into the frosting fairly easily.
Remove the frosting from the refrigerator and let it sit for couple hours until it reaches room temperature.
Microwave the frosting at 10- to 15-second intervals until it begins to melt. Avoid allowing all of the frosting to melt.
Use a whisk to whip the melted and solid frosting together until smooth and soft. If it does not soften as you beat it, return the frosting to the microwave for a few more seconds and try again.
If you over-melt the frosting, return it the refrigerator and let it chill. Once it becomes stiff, try softening it again.