preheat the oven to 350°. Butter and flour a 12 cup muffin pan or line with paper liners. Beat the flour, sugar, cocoa, eggs, butter, vanilla, and baking powder in a large bowl with an electric mixer at medium speed until well blended.
Spoon half the batter into the cups. Place a chocolate in each one. Cover with the remaining batter. Sprinkle each muffin with a few chocolate chips. Bake until a toothpick inserted into the center comes out clean, 20 to 25 minutes. Cool muffins on racks.
Makes about 12 muffins