Combine Dry Ingredients and Milk: Reduce the mixer’s speed to low and add half of the dry ingredients to the butter-sugar mixture. Mix just until combined. Then, pour in the whole milk and mix until incorporated. Finally, add the remaining half of the dry ingredients and gently mix, either on low speed or by hand. Avoid over-mixing; this will result in lighter, fluffier muffins.
Fill the Muffin Cups: Divide the batter evenly between the prepared muffin cups, filling each about 3/4 full.
Bake to Perfection: Bake for 15–20 minutes, or 8–10 minutes if making mini cupcakes. To check for doneness, insert a toothpick into the center of a muffin; it should come out clean or with just a few moist crumbs.
Cool and Enjoy: Allow the muffins to cool in the pan for about 10 minutes, then remove them and let them cool completely on a wire rack.