Heat the oven to 375°F. Grease a 12-cup muffin pan or line it with paper or foil muffin liners.
Mix together the dry ingredients (flour, sugar, salt, baking powder) in a large bowl with a mixing spoon, fork, or whisk.
In another bowl, whisk together the wet ingredients (egg, milk, and melted butter or oil) with a whisk or fork.
Pour the wet ingredients into the dry ingredients.
Using a large spoon or rubber spatula, gently combine the ingredients, stirring and folding rather than beating. Stop mixing as soon as all the dry ingredients are moistened. The batter won’t be perfectly smooth, and that’s OK. It should look thick and moist. You can add a little bit more milk if it looks too dry to you.
Spoon the batter into the muffin cups, filling them almost to the top. Bake for about 20 minutes or until nicely browned and a toothpick inserted in the center of a muffin comes out clean, or when you gently press the top of the muffins and they spring back. If you are using a square or round pan baking time is longer, 25-30 minutes. Test with a toothpick or knife, which should come out with just crumbs attached to it. If it’s wet, it needs to keep cooking.
Remove muffins from the oven and let rest for 5 minutes before taking them out of the cups.
Note: Cooled muffins can store for 2-3 days in a sealed container on the counter, or keep them in the freezer for up to 6 months, defrosting one or more muffins any time you want to enjoy them.