Place freeze-dried strawberries in a food processor or blender, and process until they resemble fine crumbs and powder. A few small chunks are fine. Set aside.
In a large mixing bowl, beat butter until creamy and smooth.
Add powdered sugar, 3 tbsp. heavy cream, vanilla extract, pinch of salt, and strawberry dust.
Beat until thick and fluffy, at least 2 minutes on medium speed.
Add additional 1 - 2 tbsp. heavy cream, as needed, to achieve desired consistency. It should be thick, fluffy, and hold shape so that it can be pipable, if needed.
Spread frosting generously onto cookies, and allow to set.
Store in airtight containers in a cool, dry place for up to a week at room temperature. If stacking cookies, layer foil or parchment paper in-between.