Preheat the oven to 350°F. Lightly grease (or line with muffin cups, and grease the muffin cups) a 12-well muffin pan., Beat together the butter, sugar, baking powder, salt, vanilla, and flavor (if you're using it) until fluffy., Beat in the eggs, then stir in the milk., Mix in the flour, then the chocolate chips., Spoon the batter into the muffin cups; they'll be quite full. Sprinkle each muffin with a little sparkling sugar., Bake the muffins for 30 minutes, or until a cake tester inserted into the center of one comes out without crumbs clinging to it (a little chocolate is OK!)., Store, well-wrapped, for 3 days at room temperature, or freeze for up to a month.