In a stand mixer, cream the butter and peanut butter together with an electric mixer until smooth and fluffy (about 2–3 minutes).
Gradually add the powdered sugar, one cup at a time, beating on low speed to avoid a sugar cloud. Scrape down the sides of the bowl as needed.
Add the vanilla extract and gradually splash in the heavy cream, milk or almond milk, beating on medium-high speed until the frosting is light, fluffy, and spreadable. Add more if needed to reach your desired consistency.
Taste the frosting and add a pinch of salt if you want to balance the sweetness. Beat again to combine.
