In a large bowl, using an electric mixer or stand mixer, cream the 1 cup unsalted butter. On low, beat in the ½ cup salted caramel sauce until combined. Beat in the 3-4 cups powdered sugar until combined, about 1 minute. Stop the mixer and scrape down the sides of the bowl. Increase the speed to medium and beat for 2 minutes until the frosting is light and fluffy.
Notes
How much frosting does it make? The recipe makes enough frosting to fill and frost an 8 or 9-inch layer cake. It is easily doubled or tripled if needed.
Use room temperature butter. Butter MUST be at soft room temperature! If your butter is too cold, it will result in a streaky frosting with lumps of butter. I like to use butter that can be pressed into with a finger with very little give. When the butter is very soft, it will whip easily and create a smooth base for the buttercream.
Beat the butter well. Start with a base of well-whipped, fluffy butter. This means that you should beat it for about 2-3 minutes, until it's lighter in color and texture.
Sift the sugar. ALWAYS sift the powdered sugar before you beat it into the frosting (this goes for a chocolate glaze or any other type of frosting, too). This will also help to make the smoothest, creamiest buttercream.
Beat in the sugar slowly. Reduce the mixer speed to low when adding the powdered sugar so that it doesn't create a huge cloud of sugar in your face! I like to add it slowly, too, so that it incorporates well.
Add sugar to taste. I like less sugar because there's sugar in the salted caramel sauce, and I like a less-sweet frosting. However, you can add more or less as you prefer.