Making these Apple Cinnamon Muffins is simple and enjoyable. Follow these steps for best results:

1. Preheat Your Oven: Set your oven to 350°F (175°C) and line a muffin tin with paper liners or grease it lightly.
2. Mix Dry Ingredients: In a large bowl, whisk together the flour, sugar, baking powder, cinnamon, and salt until well combined.
3. Whisk Wet Ingredients: In a separate bowl, beat the egg and then mix in the milk and vegetable oil. Add the vanilla extract and stir until combined.
4. Combine Mixtures: Pour the wet ingredients into the dry ingredients. Stir gently until just combined; do not overmix.
5. Add Apples: Fold in the diced apples and nuts (if using) until evenly distributed throughout the batter.
6. Divide Batter: Spoon the batter into the prepared muffin tin, filling each cup about two-thirds full.
7. Bake: Place the muffin tin in the preheated oven and bake for 20-25 minutes or until a toothpick inserted in the center comes out clean.
8. Cool: Remove the muffins from the oven and let them cool in the tin for 10 minutes. Then, transfer them to a wire rack to cool completely.

These steps will help you create fluffy and flavorful Apple Cinnamon Muffins that are sure to impress!