Prepare Raspberries: First, pulse the freeze-dried raspberries in a food processor until they turn into a fine powder. Sift this powder through a sieve to remove any seeds, then set it aside.
Make White Chocolate Ganache: In a large heatproof bowl, combine your white chocolate chips and softened butter. In a small saucepan, gently heat the heavy cream over low heat until it just begins to simmer – don't let it boil! Pour the hot cream over the chocolate and butter mixture and let it sit for about 5 minutes.
Mix & Flavor: After waiting, slowly stir the mixture until the chocolate and butter are fully melted and perfectly smooth. Now, add about ⅓ cup of your prepared raspberry powder. Stir until it's completely mixed in. Taste and add more raspberry powder if you'd like a stronger berry flavor.
Chill Ganache: Cover the bowl with plastic wrap and refrigerate for at least 2 hours, or until the mixture is firm enough to easily roll into balls.
Form Truffles: Line a baking sheet with parchment paper. Once the mixture is firm, use a heaping teaspoon to scoop out portions. Roll each portion into a smooth ball with your hands and place it on the prepared baking sheet. Repeat until you have about 24 truffles. Place the tray back in the refrigerator for 30 minutes to firm up further.
Melt Coating Chocolate: In a separate large bowl, melt the bittersweet chocolate. You can do this by using short bursts in the microwave (30-second intervals at 50% power, stirring between each) or by setting the bowl over a double boiler, stirring frequently until smooth.
Coat Truffles: Using a dipping tool or two forks, dip each chilled truffle ball into the melted bittersweet chocolate, ensuring it's fully coated. Gently tap off any extra chocolate, then return the truffle to the parchment-lined baking sheet to set.
Garnish & Enjoy: For a lovely finish, sprinkle some of the remaining raspberry powder or chocolate sprinkles on top of the truffles while the chocolate coating is still wet. Let them set completely, then enjoy your delicious homemade truffles!