Preheat your oven to 375°F (190°C) and line a muffin tin with paper liners or grease it lightly.
In a large bowl, whisk together the flour, baking soda, baking powder, ground cinnamon, nutmeg, and salt. Set aside.
In another bowl, cream the softened butter and brown sugar together until light and fluffy. This should take about 3-5 minutes.
Beat in the eggs, one at a time, followed by the vanilla extract. Mix until well combined.
Gradually add the dry ingredient mixture to the butter mixture, alternating with the milk. Start and end with the dry ingredients. Mix until just combined; do not overmix.
Gently fold in the chopped apples and walnuts or pecans (if using).
In a small bowl, mix the granulated sugar with 1 tsp of cinnamon for the topping.
Scoop the batter into the prepared muffin tin, filling each cup about two-thirds full. Sprinkle the cinnamon-sugar mixture evenly over the top of the batter.
Bake in the preheated oven for about 18-20 minutes, or until a toothpick inserted in the center comes out clean.
Allow the muffins to cool in the pan for 5 minutes, then transfer them to a wire rack to cool completely.
Enjoy warm or at room temperature, perfect for a cozy fall day!
