For the Apple Filling

1. Peel and dice the apples into small pieces (about the size of a dime) and squeeze a lemon over top and stir to combine.
2. Combine the dry ingredients and then toss together with the apples until fully coated. Pour the maple syrup over top and gently stir.
3. Heat apples on the stove over medium heat for 15-20 minutes until soft. Stir occasionally, add 1 tablespoon of water at a time as needed to prevent sticking. Cook until the apples are fork-tender and the sauce has thickened. Set aside and allow to cool before adding to the batter, refrigerating if necessary.

For the Muffins

1. Combine the dry ingredients in a mixing bowl. Set aside.
2. In a separate mixing bowl, beat the eggs until fluffy then add oil, butter, buttermilk, vanilla, and sour cream and beat until well combined.
3. Slowly add the dry ingredients and beat just until the flour starts to incorporate. Fold in the apples with a spatula and finish mixing the batter by hand. Take caution not to add too much of the apple juices to the batter. Rest the batter for 20 minutes, cover with plastic wrap.
4. Prepare the streusel by combining the melted butter with the dry ingredients until well combined. Allow the dry ingredients to absorb while the muffin batter rests.
5. Preheat the oven to 375°F. Line a 12-cup muffin pan with 6 paper liners, altering them with an empty space in between. Use a large cookie scoop to fill muffin liners to the very top. Top each muffin with streusel.
6. Bake both trays in the middle rack of the oven for 16-20 minutes. Test the muffins for doneness by inserting a toothpick into the center of the muffins. If the toothpick is clean, the muffins are done. Cool before serving.