Preheat your oven to 350°F (175°C) and prepare a muffin tin by lining it with paper liners or spraying it with non-stick cooking spray.
In a large mixing bowl, combine the all-purpose flour, granulated sugar, baking powder, baking soda, ground cinnamon, and salt. Whisk until thoroughly combined.
In a separate bowl, beat the eggs, then add the buttermilk, vegetable oil, and vanilla extract. Mix until smooth.
Gradually pour the wet mixture into the dry ingredients and gently fold until just combined.
Fold in the chopped apples and walnuts or pecans, ensuring even distribution.
Divide the batter among the muffin cups, filling each about two-thirds full.
Sprinkle a pinch of coarse sugar over the top of each muffin.
Bake for 18-22 minutes, checking for doneness with a toothpick.
Allow the muffins to cool in the tin for 5 minutes before transferring to a wire rack.
Notes
Serve warm for the best flavor. Dust with powdered sugar for an elegant touch.