Line a baking sheet with parchment. Place cocoa and crushed raspberries in shallow bowls.
Put the chopped chocolate in a medium heatproof bowl.
Warm cream and raspberry jam in a small saucepan over medium heat until steaming, stirring to dissolve the jam.
Pour hot cream mixture over the chocolate. Let stand 2 minutes, then stir from the center until smooth and glossy.
Stir in butter, vanilla, and salt until combined. Cover and chill until just firm, about 25–30 minutes.
Scoop 1-tablespoon portions and roll quickly between cool hands to form balls. Place on the lined sheet.
Roll truffles in cocoa or crushed raspberries. For dipped truffles, melt dark chocolate gently and coat, then set back on the sheet.
Chill 10 minutes to set before serving.