Place the finely chopped dark chocolate in a medium heat-proof bowl. Crush the freeze-dried raspberries into a fine powder using a spice grinder or mortar and pestle.

In a small saucepan, warm the heavy cream over medium heat until it just begins to simmer around the edges. Do not let it come to a full boil.

Pour the hot cream over the chopped chocolate and let it stand for 5 minutes without stirring. Add the raspberry powder, room temperature butter, vanilla extract, and salt. Whisk gently from the center outwards until the ganache is completely smooth and glossy.

Cover the ganache with plastic wrap, pressing it directly onto the surface. Refrigerate for at least 2 hours, or until firm enough to scoop.

Use a small cookie scoop or teaspoon to portion the chilled ganache. Quickly roll each portion between your hands to form 1-inch balls.

Place the cocoa powder in a shallow dish. Roll each truffle in the powder until evenly coated. Shake off any excess.

Serve immediately or store in an airtight container in the refrigerator for up to one week.