If you want to thicken up your runny frosting without sweetening it further with extra powdered sugar, you can reach for this ...

Cinnamon Buttercream elevates any dessert with its delightful blend of sweet and warm flavors. This American buttercream ...

If it doesn't, you can grab extra powdered sugar and start slowly ... just about ½ ounce per cup of frosting — keep this amount low if you're making a buttercream frosting.