Preheat the oven to 375°F (190°C) and line a standard muffin pan with paper liners.

In a medium-sized bowl, whisk the flour, baking powder, baking soda, salt, cinnamon, and nutmeg until well combined. In a separate large bowl, cream the softened butter and sugar together until pale and fluffy.

Add the eggs one at a time, beating thoroughly after each addition, then stir in the vanilla extract. Gradually blend the dry ingredients into the creamed mixture, alternating with the buttermilk and beginning and ending with the dry mixture. Gently fold in the diced apples until evenly incorporated.

Spoon the batter into the prepared muffin cups, filling each about two-thirds full.

Bake for 18–20 minutes, or until a toothpick inserted in the center of a muffin emerges clean. Allow the muffins to cool in the tin for 5 minutes before transferring to a wire rack to cool completely.