A smooth, flawless finish with buttercream isn’t unattainable, but it does require some work. While some decorators use fondant for a flawless finish, you can get a smooth, satin-like finish with just buttercream. If you’ve ever tried to frost a round cake with buttercream, you already know the unique challenges, especially on the edges. However, you can get a flawless finish and you don’t have to be a professional cake decorator to do it.
Set your stacked round cake on a decorating turn table. If you don’t have a decorating turn table, elevate your cake on a turned over bowl, but make sure it’s steady.
Apply a crumb coat to the surface of your cake. A crumb coat is a thin layer of buttercream that holds any lingering crumbs in place and prevents crumbs from getting into your final layer of buttercream. The crumb coat should hug the sides and top of your cake and you should see some cake through the crumb coat. Allow the crumb coat to firm up until it’s no longer tacky to the touch.
Using a piping bag, pipe in even layers up and down the sides of your cake, covering every inch. Continue around the sides until you no longer see any cake.
Starting at the center of the top of your cake, pipe out buttercream in a spiral motion until the entire top surface of your cake is covered.
Bring water to a boil on the stove using a saucepan or tea kettle. It’s best to keep your water boiling while you use it, since you need very hot water throughout the frosting process.
Dip the decorating edge of your angled spatula or pastry blade into the hot water and wipe clean. Slightly angle the edge of the decorating tool against the side of the cake and pull the blade toward you in a smooth, slow manner. Carefully pull the spatula toward you to remove it from the cake, dip it back in the water, dry and repeat until all sides of the cake are smoothed down. Don’t worry about bubbles or slight imperfections at this point.
Start the decorating tool at the top edge of your cake after you’ve dipped it in hot water and dried it again. Carefully pull the buttercream from the outer edge toward the top center. Turn your cake and repeat the process until the buttercream is smooth on the top of the cake and the buttercream is smoothed off the edge.
Take a piece of parchment paper and gently place it along the side of your cake. Using the palm of your hand or a fondant smoother to smooth in a circular motion over the parchment paper. Repeat on all sides. Don’t apply too much pressure, because this can leave imprints in your buttercream finish.
Lay a new piece of parchment paper on the top edge of the cake. Focus your smoothing on the rim by smoothing from the sides over the edge and toward the top center of the cake.
Use a clean piece of parchment paper and smooth the top center of the cake using your hand or fondant smoother.
Inspect the cake’s surface for any air bubbles. Use parchment paper to slowly rub the air bubbles toward the bottom edge or top edge of the cake until they’re no longer present. Look for any areas that need touch-up smoothing and use your parchment paper to smooth them out.