Double Chocolate Chip Muffins

Center a rack in the oven and preheat to 375°F. Butter or spray the 12 molds in a regular-size muffin pan or fit the molds with silicone or paper muffin liners. Place the muffin pan on a baking sheet.

Melt the butter and half the chopped chocolate together in a bowl over a saucepan of simmering water; or do this in a microwave. Remove from the heat.

In a large bowl, whisk together the flour, sugar, cocoa, baking powder, baking soda, and salt. In a large glass measuring cup or another bowl, whisk the buttermilk, egg, and vanilla extract together until well combined. Pour the liquid ingredients and the melted butter and chocolate over the dry ingredients and, with the whisk or a rubber spatula, gently but quickly stir to blend. Don't worry about being thorough—a few lumps are better than overmixing the batter. Stir in the remaining chopped chocolate. Divide the batter evenly among the muffin cups.

Bake for 20 minutes, or until a thin knife inserted into the center of the muffins comes out clean. Transfer the pan to a wire rack and cool 5 minutes before carefully removing each muffin from its mold.