In a glass bowl over simmering water or in the microwave, melt the chocolate and butter together. Allow to cool, but not harden.
In a small bowl, whisk together the eggs, vanilla extract, and sugar. Add this mixture to the melted chocolate. Stir to combine.
Stir in the flour and baking powder until combined. Cover and chill in the refrigerator for at least 30 minutes up to overnight.
Spoon or scoop onto a baking sheet with a baking mat or parchment paper. Add sprinkles if using. Bake at 350°F for 9-10 minutes (the centers should look slightly raw). Allow to cool for a few minutes on the baking sheet then remove to a cooling rack.