Gather the ingredients. Preheat the oven to 425 degrees F (220 degrees C). Line 6 large (3½-inch) muffin cups with paper muffin liners.

To make the muffins: Stir flour, sugar, baking powder, cinnamon, and salt together in a large bowl. Mix in egg, oil, and milk. Fold in chopped apples.

Spoon ½ cup of batter into each muffin liner.

To make the streusel topping: Place sugar, flour, butter, and cinnamon into a small bowl; mash mixture with a fork until mixture begins to cling together. Sprinkle topping evenly over unbaked muffins.

Bake in the preheated oven for 5 minutes. Reduce oven temperature to 350 degrees F (175 degrees C) and bake until a toothpick inserted into the center of a muffin comes out clean, 25 to 30 minutes. Let cool in pan briefly; remove muffins and cool on a wire rack.

Enjoy!