Heat oven to 375°F. Line a 12-cup muffin pan and lightly grease the liners.
Whisk flour, baking powder, baking soda, salt, cinnamon, and nutmeg in a medium bowl.
Whisk eggs with both sugars in a large bowl until slightly thick and glossy.
Add milk, oil, and vanilla. Whisk until smooth and well combined.
Stir in the dry mixture just until no dry spots remain. Do not overmix.
Fold in diced apples and walnuts gently to distribute evenly.
Scoop batter into liners, about 3/4 full. Sprinkle tops with turbinado sugar.
Bake 18–21 minutes, until golden and a toothpick comes out clean.
Cool in pan 5 minutes, then move muffins to a rack to finish cooling.
Notes
Try swapping walnuts with pecans, or stir in a handful of raisins. For extra moisture, replace 2–3 tablespoons of milk with applesauce. Store airtight at room temperature for 2 days, or freeze up to 2 months. Warm before serving and add a pat of butter or a drizzle of honey.This recipe is an original creation inspired by classic Apple Walnut Muffins flavors. All ingredient ratios and instructions are independently developed.