1/2 cup unsalted butter, at room temperature
1/2 cup granulated sugar
3/4 cup brown sugar, divided use
1 large egg
1 cup buttermilk (or mix together 3/4 cup Greek-style yogurt and) 1/4 cup milk
1 cup whole wheat flour
1 cup unbleached all-purpose flour
1 teaspoon baking powder
1 teaspoon baking soda
1/4 teaspoon salt
1 tablespoon ground cinnamon
2 cups peeled, cored, and chopped Golden Delicious apples (about 2 large apples)
Preheat oven to 375°F. Grease and flour a 12-cup muffin pan, or line with paper linerss and grease the insides of the papers with cooking spray.
In a large mixing bowl, cream the butter, granulated sugar, and 1/4 cup of the brown sugar, using a hand mixer until fluffy.
Add the egg and mix well, stopping once to scrape the sides and bottom of the bowl. Gently mix in the buttermilk.
Combine the flours, baking powder, baking soda, salt, and cinnamon and add to wet ingredients. Fold in the chopped apples.
Divide the batter evenly among the prepared muffin cups, sprinkling the remaining 1/2 cup brown sugar on top.
Bake for 25 to 30 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Remove the muffins from the oven, cool them for 5 minutes in the pan, then turn them out onto a rack to finish cooling completely. Makes 12 muffins.