Preheat oven to 375°F and line or grease a 12-cup muffin pan.

In a large bowl, whisk together flour, sugar, baking powder, and salt until evenly combined and free of lumps.

In another bowl, whisk the egg, oil, and milk until the mixture is smooth and fully blended.

Pour the wet ingredients into the dry ingredients. Stir gently using a spoon or spatula until a thick batter forms. Do not overmix; a slightly lumpy batter is ideal.

Add chopped peaches and fold them into the batter carefully so they are evenly distributed without breaking down too much.

Divide the batter evenly into the muffin cups, filling each about 3/4 full to allow room for rising.

Bake for 18 to 22 minutes, or until the tops are golden and a toothpick inserted into the center comes out clean.

Let muffins cool in the pan for 5 minutes, then transfer to a rack to cool slightly before serving.