First, place your chocolate truffles in the freezer.
In a large bowl, cream together the butter and sugar until light and creamy.
Add in the egg, mixing until fully incorporated, then mix in the vanilla. Add in the cocoa powder, baking powder, and salt, and mix. Then, add in the flour, and mix again.
Refrigerate dough for 20-30 minutes.
When ready to bake, preheat oven to 350F.
Line 2 baking sheets with parchment/silicone, and scoop tablespoonfuls of dough onto them at 12 per sheet. Bake 10-12 minutes, until cookies appear slightly dry on top. They will seem soft, but should set upon cooling.
As soon as you remove the cookies from the oven, press a frozen truffle in the center of each.
Let cookies cool to room temperature to set, and enjoy!