Place the freeze-dried raspberries in a food processor and blend until it forms a fine powder. Then, use a fine-mesh sieve to sift the raspberry powder into a small bowl, reserving about 2 teaspoons for garnish later.

In a large heatproof bowl, combine the chopped white chocolate and butter.

In a small saucepan, heat the heavy cream over low heat until it just begins to simmer, then pour it over the chocolate mixture, letting it sit for 5 minutes without stirring.

Gently stir the chocolate mixture until completely smooth. Add the raspberry powder one tablespoon at a time, whisking well after each addition.

Cover the bowl with plastic wrap and refrigerate for about 2 hours, or until the mixture is firm enough to scoop.

Line a baking sheet with parchment paper. Use a small scoop or spoon to portion out the mixture, rolling it into balls and placing them on the prepared sheet.

Chill again for 30-45 minutes until firm.

While the truffles chill, melt the bittersweet chocolate over a double boiler or in the microwave, being careful not to burn it.

Using a fork, dip each truffle into the melted chocolate, allowing any excess to drip off.

Sprinkle the reserved raspberry powder over the dipped truffles before they set. Let them cool at room temperature or place them in the fridge briefly.

Store the truffles in an airtight container in the refrigerator for up to 1 week or freeze for longer storage.