Place the freeze-dried strawberries in a food processor or blender. Process on high until they form a fine powder. This usually takes 30-60 seconds. Set aside.

In the bowl of a stand mixer fitted with the paddle attachment, beat the softened unsalted butter on medium-high speed for 2-3 minutes, until light and fluffy. Scrape down the sides of the bowl.

Gradually add the sifted powdered sugar, about 1 cup at a time, mixing on low speed until combined after each addition. Once all sugar is added, increase speed to medium and beat for another 1-2 minutes.

Add the prepared freeze-dried strawberry powder, marshmallow creme, vanilla extract, and salt to the butter mixture. Start with 2 tablespoons of heavy cream or whole milk.

Beat on medium-high speed for 3-5 minutes, scraping down the bowl as needed, until the frosting is light, fluffy, and evenly colored. If the frosting is too thick, add the remaining heavy cream or milk one tablespoon at a time until desired consistency is reached. If it's too thin, add a tablespoon or two of additional sifted powdered sugar.

Use immediately to frost cakes, cupcakes, or other baked goods.