In a large mixing bowl, combine 1 1/2 cups of all-purpose flour, 1/2 cup of whole-wheat flour, 2 teaspoons of baking powder, 1/2 teaspoon of baking soda, and 1/2 teaspoon of salt. Set aside.
In another bowl, whisk together 1 cup of buttermilk, 1/2 cup of unsalted melted butter, 2 large eggs, and 1 teaspoon of vanilla extract.
Pour the wet ingredients into the dry ingredients, and gently mix until combined. Be careful not to overmix.
Preheat your oven to 350°F (175°C). Line a muffin tin with paper liners.
Divide the batter evenly among the muffin cups, filling each about two-thirds full.
Bake for 20-25 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Allow the muffins to cool in the tin for 5 minutes, then transfer them to a wire rack to cool completely.
Enjoy these delicious whole wheat apple muffins as a breakfast treat or snack.