Smoothly frosting cakes is easiest when you start with creamy smooth icing. The consistency of your icing should be similar to whipped cream. It should be light and fluffy without air bubbles. Use a planetary action mixer to create creamy smooth icing (mixers that only use one paddle). Fill the bowl with the mixture and then cover it with icing. Use the paddle attachment to buttercream, not the whisk. Mix on low speed for 3 to 5 minutes or until no air bubbles are visible. Don't overmix. Mix the icing at half speed if your mixer has standard beaters. To avoid air bubbles, beat your icing at the slowest speed.A smooth frosting can be achieved if a cake has been frosted with creamy smooth cream icing. This is possible by using a small spatula or icing instrument held at an angle so that only one side of the icing touches the cake's surface. Start by smoothing the sides, then the top. Work from the outside towards the center. Use long, smooth strokes to feather the edges. After each stroke, clean the spatula. This technique is great when you use the right consistency of icing. However, practice makes perfect.

Other methods

These methods allow for less consistent icing.

Paper Towel, or Paper Smoothing Method

You can use certain brands of paper towels to create a smooth surface for buttercream icings that has crusts. Your icing will dry to a smooth surface so no icing is left on your hands when you touch it. Let the iced cake cool to dry. Refrigerating it will make it stay moist. The humidity will determine how long it takes. It takes longer if there is more humidity. Let's say it takes 5-10 minutes. You should look for paper towels without texture. There are only a few texture-free paper towel brands available, and each brand is different in every region. Keep your paper towels for smoothing frosting in a container that won't attract any lint. A large Ziploc bag. Use a spatula to smoothen the icing. Allow the icing to set for about 15 minutes. You can test a small area of the icing by placing your hand on a piece of dry paper towel. You can try rubbing the icing with a paper towel on a small area. Do not use your fingers to create ridges. This will remove air bubbles and spatula marks, creating a smooth surface. The same process can be used with waxed or parchment paper, but you may need to wait for the icing to dry. You can also smoothen the icing with waxed or parchment paper again after you have used the paper towels.

Water Smoothing

There are two methods to smoothen water. 1. Frost the cake as normal and use a dry spatula to smoothen it. Use a large spatula to dip in hot water. The spatula should be held at an angle so that only one side touches the icing. First, smoothen the sides of your cake. From the outside edge, smoothen the top of your cake toward the center. Use long, smooth strokes to feather the cake towards the center. After each stroke, dry the spatula and then rewet it. Make sure to not over-wet icing. The color of icing can streak. 2. Spray the icing with a spray bottle and then use a spatula to skim across the surface, as described above. After each stroke, wipe the spatula clean. Make sure to not over-wet icing. The color of icing can streak.

It is important to empty your spray bottles every day if you use them to smooth your icing. Use a dish soap and water to rinse the bottle. Allow it to dry in the air. It is not a good idea to spray "contaminated" water onto your cakes. In a commercial kitchen, this is something that the Health Department would look out for.

How do you achieve a smoothly frosted cake?