Whisk the butter, sugar, and egg together until homogeneous. Crush the freeze-dried raspberries into a fine powder, mix with the flour, and add to the first mixture. Work until the dough forms a ball.
Preheat your oven at 350°F/180°C. Flour a clean, flat surface and roll out the dough until it is 1/16 of an inch. Flour your hands and rolling pin as well if it sticks. Cut shapes using cookie cutters, and transfer them to a baking pan covered in parchment paper.
Bake for 10 min or so, until the edges start darkening. Take out and let cool before eating. The cookies should harden and become crunchy.
You can substitute any freeze-dried berry of your choice for the raspberries in this recipe, or even use 100% dark cocoa powder.