Place the cream cheese and mascarpone into a mixing bowl along with sifted powdered sugar then slowly start whipping up the mixture with an electric hand mixer.
Increase the speed of your mixer, and continue whipping.
Just before the mixture starts to thicken, add the vanilla extract and smooth peanut butter to the mixture and continue whipping.
When the frosting reaches a fluffy, pipeable consistency, stop right there and do not overmix. If you continue whipping the frosting, it will separate and gets runny.
Use the frosting according to the recipe.
Store refrigerated for 3 days in an airtight container
Notes
The frosting is enough to frost about 9-10 cupcakes or a smaller size two layer cake.Ingredient notes:
Measure your ingredients with a digital scale for accuracy.
The cream cheese and mascarpone both need to be high in fat. Using the low-fat version may result in a thinner frosting since it contains more water.
Mascarpone can be substituted with an equal amount of very cold, 36% heavy cream.
Use only smooth peanut butter, preferably unsweetened. If using sweetened peanut butter, reduce the powdered sugar in the recipe
Technique notes:
Make sure you read my Expert tips section above to maximize your success. A short recipe alone is not able to cover all the necessary details and science behind baking.
Cream cheese frosting is very easy to overwhip. When whipping the frosting, stop as soon as the mixture reaches a fluffy consistency (will take 2-3 minutes). It won´t get stiffer after this point. In fact, if you overwhip it, it will only get runnier, and then it will break.
I prefer to use an electric hand mixer as opposed to a stand mixer to make this frosting. If using a stand mixer, whip the frosting up at medium speed, and do not walk away from the mixer.