Stir together butter powder and water.
Blend butter on medium-high speed 6 to 7 minutes or until creamy and smooth.
On low speed, slowly add powdered sugar, continue beating until sugar is fully incorporated.
Add in vanilla and cream (or milk) and mix on low speed until incorporated.
Return to medium-high speed and beat the buttercream for an additional 6 to 7 minutes.
If buttercream is too thick, add one teaspoon of milk at a time until desired consistency is reached.
