Whole Wheat Apple Muffins

Steven said he wouldn't mind muffins for breakfast today, but they had to be "good" ones. So, I googled "best ever muffins" and found a plethora of possibilities. I settled on this one from Smitten Kitchen, although I also saw it at a few other websites. And it was a success. Apparently, there was enough sugar to overcome the fact that it contained wheat flour!
Whole Wheat Apple Muffins
Adapted from King Arthur Flour

1 cup whole wheat flour
1 cup all-purpose flour
1 teaspoon baking powder
1 teaspoon baking soda
1/4 teaspoon salt
1 tablespoon cinnamon
1/2 cup butter or margarine
1/2 cup granulated sugar
1/2 cup brown sugar, packed, divided
1 large egg, lightly beaten
1 cup (8 ounces) buttermilk or yogurt (Since I don't keep this on hand, I added a tablespoon of vinegar to just under a cup of milk and let it sit for a few minutes.)
2 large apples, peeled, cored, and coarsely chopped (1 was enough for our family)

Preheat the oven to 450°F. Grease muffin cups and set aside.

Mix together the flours, baking powder, baking soda, salt, and cinnamon, and set aside. In a separate bowl, cream the butter and add the granulated sugar and 1/4 cup of the brown sugar. Beat until fluffy. Add the egg and mix well; stop once to scrape the sides and bottom of the bowl.Mix in the buttermilk gently. (If you over-mix, the buttermilk will cause the mixture to curdle.) Stir in the dry ingredients and fold in the apple chunks.

Divide the batter evenly among the prepared muffin cups, sprinkling the remaining 1/4 cup brown sugar on top. Bake for 10 minutes, turn the heat down to 400°F, and bake for an additional 5 to 10 minutes, or until a toothpick inserted into the center of a muffin comes out clean. Cool the muffins for 5 minutes in the tin, then turn them out onto a wire rack to cool completely. Yield: about 12