In a large bowl, beat the softened butter with an electric mixer until smooth and creamy.
Add powdered sugar, one cup at a time, mixing well after each addition.
Pour in the raspberry puree, vanilla extract, and salt. Beat on medium speed until fully combined and fluffy.
If the frosting seems too thick, add a teaspoon of milk. If too thin, add a bit more powdered sugar.
Spread or pipe onto cooled cupcakes and enjoy.