Pistachio Buttercream is a light and fluffy frosting made with just four simple ingredients, including a package of pistachio pudding mix.
Add butter to the bowl of a stand mixer (or use a handheld mixer) and beat on medium speed until creamy, about 1 minute.
Turn off mixer and add all the pistachio pudding mix and 1 cup of confectioners' sugar. Mix on low until ingredients are incorporated.
Alternating the milk with the remaining sugar, add a tablespoon of milk at a time and a ½ cup of confectioners' sugar at a time until all ingredients are incorporated.