Chop the semisweet chocolate finely and place it in a heatproof bowl.
Heat the heavy cream in a small saucepan until it just begins to simmer.
Pour the hot cream over the chopped chocolate and let it sit for 2 minutes.
Stir gently until the chocolate melts and the mixture is smooth.
Add the bourbon and butter to the chocolate mixture and blend until fully incorporated.
Cover the bowl with plastic wrap and chill in the refrigerator for at least 2 hours until firm.
Use a teaspoon or a melon baller to scoop out small portions of the truffle mixture.
Roll the truffle portions between your palms to form smooth balls.
Roll each truffle ball in unsweetened cocoa powder to coat.
Place the coated truffles on a baking sheet lined with parchment paper and refrigerate until firm.
Notes
Store truffles in an airtight container in the refrigerator for up to 1 week. Let them sit at room temperature for 10 minutes before serving for the best texture.