Puree the raspberries in a blender or food processor until smooth. Strain the puree through a fine mesh sieve to remove seeds, and let it cool completely for the best flavor.

Beat the unsalted butter in a large mixing bowl using a hand mixer or stand mixer for 3 to 5 minutes, until it's pale and fluffy.

Add the powdered sugar gradually, one cup at a time. Mix well after each addition.

Pour in the cooled raspberry puree, vanilla extract, and a pinch of salt. Beat until light and smooth.

Adjust the consistency: Add more raspberry puree or milk if too thick; more powdered sugar if too thin.

Frost immediately on your favorite cakes, cupcakes, or cookies.