01 - Set oven to 375°F. Line a 12-cup muffin tin with paper liners or grease lightly.
02 - In a large bowl, whisk together flour, sugar, baking powder, baking soda, and salt until thoroughly blended.
03 - In a separate bowl, beat the eggs. Whisk in milk, oil or melted butter, and vanilla extract until uniform.
04 - Make a well in the center of the dry ingredients. Pour in the wet mixture and fold gently until just combined, avoiding overmixing.
05 - Fold in your choice of berries, chocolate chips, or nuts, if desired.
06 - Evenly distribute the batter into the prepared muffin tin, filling each cup about three-quarters full.
07 - Bake for 18 to 22 minutes, or until a toothpick inserted in the center emerges clean.
08 - Allow muffins to cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.