Let the Frosting Set: Allow the frosting to fully set and harden before stacking the cookies. This can take anywhere from 1-2 hours at room temperature. If you’re in a hurry, you can speed up the process by placing the cookies in the refrigerator for 20-30 minutes. Use Parchment or Wax Paper: When stacking cookies in a container, place a sheet of parchment paper or wax paper between each layer. This creates a barrier that prevents the frosting from sticking to the cookie above. Store in a Single Layer: If possible, store the cookies in a single layer in an airtight container. This eliminates any risk of them sticking together.