How to Make It
Prepare the Cookies: Preheat oven to 350°F. Line 2 rimmed baking sheets with parchment paper. Stir together cake mix, eggs, oil, freeze-dried strawberries, and baking powder in a large bowl.
Shape dough into 30 (1 1/2-inch) balls; place on prepared baking sheets about 2 inches apart. Freeze 10 minutes.
Bake in preheated oven, until just before turning golden, about 9 minutes. Transfer baking sheets to a wire rack; cool cookies on baking sheets, 5 minutes. Transfer cookies directly to wire rack; let cool completely, about 30 minutes.
Prepare the Frosting: Process chopped strawberries in a food processor or blender until smooth. Set aside.
Beat butter with a heavy-duty stand mixer fitted with a paddle attachment on medium speed until creamy, about 1 minute. Gradually add powdered sugar until well incorporated. Add vanilla, salt, and pureed strawberries, beating on medium speed until mixture is creamy, about 1 minute. Increase speed to medium-high; beat until light and fluffy, about 1 minute. Fold in the crushed freeze-dried strawberries.
Transfer frosting to a piping bag with a star tip. Pipe Strawberry Frosting on 15 of the cooled Vanilla Cookies; top with remaining cookies. Garnish with crushed freeze-dried strawberries.