Method

• Prepare the oven and pan: Heat the oven to 400°F (205°C). Line a 12-cup standard muffin pan with paper liners or lightly grease each cup. Peel and core the apple, then dice it into roughly 1/4-inch pieces.
• Combine dry ingredients: Whisk the flour, cornmeal, sugar, baking powder and salt in a large bowl until evenly distributed. Break up any visible baking-powder lumps.
• Whisk wet ingredients: In a second bowl, whisk the buttermilk, eggs and oil until the eggs are fully blended.
• Mix briefly and add apple and cheese: Pour the wet mixture into the dry ingredients and fold just until the dry flour is nearly incorporated. Fold in the diced apple and 3/4 cup cheddar until evenly distributed, stopping as soon as no dry pockets remain. Small lumps are fine.
• Fill and bake: Divide the batter among the 12 cups, filling them about three-quarters full. Sprinkle the remaining 1/4 cup cheddar over the tops. Bake for 18–22 minutes, until the tops are golden and a tester inserted into the crumb comes out without wet batter. Avoid confusing melted cheese with uncooked batter; check a second spot if needed.
• Cool before serving: Let the muffins rest in the pan for about 5 minutes, then transfer them to a rack for another 5 minutes before serving.