Finely chop the dark chocolate into small, evenly sized pieces and place them in a heatproof bowl. Smaller pieces melt more evenly and help prevent unwanted lumps in your truffle mixture.

Pour the heavy cream into a small saucepan and warm it over medium-low heat until it becomes hot and small bubbles begin forming around the edges. Avoid bringing it to a full boil. Remove the saucepan from the heat.

Pour the warm cream over the chopped chocolate. Let everything sit undisturbed for about 2 minutes, allowing the chocolate to soften. Gently stir from the center outward until the mixture becomes smooth and glossy. Add the butter and vanilla extract, then stir until fully incorporated. Your chocolate ganache should look thick, silky, and free of lumps.

Cover the bowl with plastic wrap or a suitable lid and place it in the refrigerator for approximately 2 hours. The ganache needs enough time to become firm but still soft enough to scoop. If it feels too sticky to handle, leave it in the refrigerator for another 15–20 minutes.

Once the mixture is firm, use a teaspoon or small cookie scoop to portion it into approximately 18–20 equal pieces. Quickly roll each portion between your palms to form small, round balls. If the mixture starts sticking to your hands, chill it again briefly before continuing.

Place the cocoa powder in a shallow bowl and gently roll each chocolate ball until completely coated. Arrange the finished truffles on a serving plate or in mini paper candy cups. Refrigerate them for another 15–20 minutes if you prefer a firmer texture.