In a medium-sized bowl, whisk together cocoa powder, flour, and salt. Set aside.
In a large mixing bowl, or using a kitchen mixer, beat together sugar, 8 tbsp of butter, and vanilla, until light and fluffy (approximately 3 minutes).
Slowly add dry ingredients to wet a little at a time, and alternate with milk. Using a mixer, continue to mix until the dry ingredients are completely incorporated into a thick batter.
Roll the batter into small balls that are 1 - 1.5 inches thick. Place the cake batter balls onto parchment paper. For best results, refrigerate for at least 30 minutes before dipping in chocolate.
Prepare your chocolate shell: melt your semi-sweet chocolate and 1 tbsp butter in a microwave-safe bowl in 30-second intervals. Alternatively, heat on the stove over a double boiler.
Place a toothpick through the top of the cake batter balls, and dip them into the chocolate (you can also use a fork). Completely coat and set on parchment paper to dry. Sprinkle any toppings on the truffles.
Completely dry at room temperature for at least an hour before serving. You can also refrigerate for 30-40 minutes or freeze for approximately 20 minutes. Once dried, remove toothpicks and serve!