Peel and dice about 1 ½ apples into ½ inch chunks. You want 2 cups diced apples. Set aside.
In a mixing bowl combine the flour, granulated sugar, brown sugar, cinnamon, baking powder, and salt. Stir with a spoon to combine and set aside.
3 cups (360g) all purpose flour, 1 cup (198g) granulated sugar, 1/2 cup (107g) brown sugar, 2 tsp cinnamon, 2 tsp baking powder, ½ tsp salt
In a larger mixing bowl combine the eggs, buttermilk, vegetable oil, and vanilla extract. Stir to combine with a fork or spatula.
2 large eggs, ¾ cup (170g) buttermilk, ½ cup (100g) vegetable oil, 2 tsp vanilla extract
Gradually mix in the dry ingredients and the apple chunks, mixing just until combined. The batter will be very thick!
2 cups diced apples
Cover the bowl with a towel and allow the batter to rest for 15 minutes. During this time, preheat the oven to 425ºF.
For bakery style muffin tops, line a 12 count muffin pan with 6 muffins liners, meaning you’ll only fill every other muffin well with batter. Filling every other well allows the muffins to spread and dome without running into each other. Fill the liners to the top with batter. Yes – to the top! Use a butter knife to smooth the tops of the muffins if lumpy.
Bake for 7 minutes at 425ºF, then keep the muffins in the oven, and turn the temperature down to 350ºF and bake for 16-21 minutes or until a toothpick inserted in the center comes out clean. Allow the muffins to cool in the pan for 15 minutes before removing. Repeat with the remaining batter, making sure to bump the temperature back up to 425ºF.
Once the muffins are cool, assemble the cinnamon sugar topping. Melt 2 tablespoons of butter. Use a pastry brush to brush the melted butter on top of the muffins. Roll the top of each muffin in a bowl of cinnamon sugar.
Gluten-Free: Use a 1:1 gluten-free baking flour blend in place of all-purpose flour. I used King Arthur's Measure for Measure Gluten Free Flour with great results.To Store: Leave muffins uncovered on the counter for up to 24 hours. For 2 to 4 days, store in an airtight container lined with paper towels, with another layer of paper towels on top. Swap in fresh paper towels if they get damp.To Make Ahead: This batter can be made ahead of time. Cover and refrigerate it for up to 24 hours, then scoop straight from cold and bake as directed. You may need to add a couple extra minutes to the bake time since the batter is starting out cold.To Freeze: Wrap each cooled muffin individually in plastic wrap, then place in a zip top bag or airtight container. Freeze for up to 3 months. Thaw on the counter for about 1 hour, or unwrap and microwave in 20 second intervals.