Prepare: If using fresh or frozen strawberries, puree them in a blender until smooth. For a seedless frosting, strain the puree through a fine-mesh. You should have about 1/2 cup of puree. If using freeze-dried strawberries, grind them into a fine powder using a food processor. No need to strain.

In a large mixing bowl, beat the softened butter with an electric mixer on medium speed until creamy, about 2 minutes. The butter needs to be soft but not melty.

Incorporate Dry Ingredients: Gradually add the powdered sugar, 1 cup at a time, beating on low speed after each addition. This will help prevent a powdered sugar snowstorm in your kitchen. Once all the sugar is incorporated, add the salt and vanilla extract (if using), and beat on medium speed until fully combined.

Add the Strawberry Flavor: For fresh or frozen strawberry puree, beat in the puree on low speed until just combined. If the frosting is too thin, you can add a bit more powdered sugar. For freeze-dried strawberry powder, mix in the strawberry powder until evenly distributed. If the frosting is too thick, add heavy cream or milk, one tablespoon at a time.

Final Touches: Increase the mixer speed to high and whip the frosting for an additional 2-3 minutes until light and fluffy. This will incorporate air into the frosting.