In the bowl of a stand mixture, or a large bowl, cream butter and shortening together until light and fluffy.
Add powdered sugar, vanilla, and 1 Tablespoon cream to the butter mixture.
Mix until incorporated.
Mix on high for 3-5 minutes, until buttercream is silky, smooth, and fluffy. If needed, add up to one additional Tablespoon of cream to thin and achieve the desired consistency.
Notes
Leftovers will keep in an airtight container for 3 days and in the freezer for 3 months.