Place chopped dark chocolate in a heatproof bowl.

In a small saucepan, heat heavy cream and butter over medium heat until it just begins to simmer.

Pour the hot cream mixture over the chocolate and let sit for 2 minutes.

Stir gently until smooth and fully melted.

Mix in raspberry jam and vanilla extract until fully combined.

Cover and refrigerate the mixture for at least 2 hours, or until firm enough to scoop.

Using a small scoop or spoon, portion out the truffle mixture and roll into balls.

Roll each truffle in cocoa powder to coat.

Store in an airtight container in the refrigerator until ready to serve.

Garnish with fresh raspberries just before serving, if desired.