Preheat the oven to 375°F. Line or grease a muffin pan.
In a large bowl, stir flour, sugar, baking powder, and pudding mix.
In another bowl, whisk eggs, milk, oil, and extract.
Combine wet and dry ingredients gently—don't overmix.
Fold in mix-ins (chocolate chips, fruit, or nuts).
Fill muffin cups halfway with batter. Add a spoonful of pudding filling in the center.
Cover with more batter until almost full.
Bake for 18–22 minutes. Test with a toothpick.
Let cool before serving.