Canned frosting has an ideal consistency for spreading onto cakes as a crumb coat or regular frosting coat, but it is not thick enough to use for decorating or adding designs onto a cake. You can modify canned frosting by adding icing sugar to it so that it becomes thick enough to use for decorations. Icing sugar stiffens the frosting and makes it thick enough to hold the shape of designs when using decorating tips and a pastry bag. The addition of the sugar will also make the frosting much sweeter, so make sure to compensate for the additional sweetness by using a little less sugar in your cake recipe.
Scoop the frosting out of the can using the spatula and place it in the bowl of the stand mixer.
Add 1/2 cup icing sugar to the frosting. Mix the sugar into the frosting with the spatula before turning on the mixer.
Secure the beater attachment to the mixer and turn the mixer on low, gradually increasing the speed to the highest setting. Mix the frosting for about 2 minutes, then turn off the machine.
Lift the beater out of the frosting. If the frosting adheres to the beater and does not slide off when you shake it, it is stiff enough. If it does not hold its shape, then you need to add more sugar to the frosting. Continue to add more sugar in 1/2-cup increments until it is stiff.
If you do not have a stand mixer with a flat beater attachment, a hand mixer will also work for mixing the frosting with the icing sugar.