Put the chocolate in a stainless-steel or glass bowl.

Pour the cream into a heatproof container and heat in the microwave until just boiling, about 1 minute. Alternatively, pour the cream into a small saucepan and heat on the stovetop until just boiling. 

Pour the hot (not boiling) cream over the chocolate. Put the butter pieces on top of the cream and let sit for a few minutes, then whisk until the ingredients are incorporated and the mixture is smooth. If everything did not melt down, carefully microwave for less than 30 seconds. Add the raspberry preserves and whisk to combine. Cover with plastic wrap and refrigerate until slightly firm.

Put the cocoa powder in a bowl. Line a baking sheet with parchment paper or plastic wrap.

Using a teaspoon (not a measuring teaspoon), scoop out the truffle mixture and quickly roll with your hands into a ball. Place on the prepared baking sheet. Transfer to the freezer for 10 minutes to set. Do NOT freeze for longer.

Remove the truffles from the freezer. Line another baking sheet with parchment paper or plastic wrap. Toss the truffles, a few at a time, in the cocoa powder, then roll each one around again with your hands. Place on the clean parchment or plastic wrap and refrigerate until set

When the truffles are set, transfer them to an airtight container and refrigerate for up to 2 weeks. Remove from the refrigerator 30 minutes before serving. 

The truffles also freeze well: Line an airtight container with plastic wrap and place the truffles inside. Cover the truffles completely with the plastic wrap. Place the lid on the container, then wrap the entire container in plastic wrap and freeze. To thaw, remove the container from the freezer and let stand at room temperature for at least 3 hours, keeping it wrapped in the original packaging. Then put the container in the refrigerator. This will prevent condensation from forming on the chocolate.