Divide the batter among 12 paper-lined muffin cups, about 3/4 full. Sprinkle with the chocolate chips. Bake for 15-17 minutes, rotating once, until the muffin tops look set, and a cake-tester inserted into the center of the muffins comes out clean. Remove from the oven and let cool in the muffin tin for 5 minutes, before removing and cooling completely on a baking rack. Serve warm or at room-temperature.