• 1/2 cup butter, melted or neutral oil
• 1/3 cup granulated sugar
• 1/3 cup packed light brown sugar
• 1/3 cup buttermilk
• 1 large egg
• 1 teaspoon vanilla extract
• 1 2/3 cups all-purpose flour or white whole wheat flour
• 1 teaspoon baking powder
• 1 teaspoon cinnamon
• 1/4 teaspoon baking soda
• 1/4 teaspoon salt
• 1 1/2 cups small-diced sweet-tart apples
• Coarse sugar, turbinado sugar, or brown sugar, for sprinkling (optional)

Preheat the oven to 350°F. Line a 12-cup muffin tin with paper liners and set aside. In a large bowl, whisk together the melted butter, granulated sugar, brown sugar, buttermilk, egg, and vanilla extract until smooth and well combined. Add the flour, baking powder, cinnamon, baking soda, and salt, stirring just until combined; a few dry streaks are fine. Fold in the diced apples, being careful not to overmix the batter. Divide the batter evenly among the muffin cups, filling each about two-thirds full. Sprinkle the tops with coarse sugar, turbinado sugar, or brown sugar, if desired. Bake for 17–18 minutes, or until the tops spring back lightly when touched. Allow the muffins to cool in the pan for a few minutes before transferring to a wire rack to cool completely. These muffins are delicious served warm, but the flavor deepens even more as they cool.