Preheat the oven to 375℉. Line a muffin tin with muffin liners and set aside. Chop the apples into small pieces and set aside.
In a small bowl, make the streusel. Combine flour, white sugar, brown sugar, cinnamon, and cold cut up butter. Using your hands, mix it together until combined into a crumbly, streusel mixture. Set aside while you make the muffin batter.
1/2 cup flour, 1/4 cup light brown sugar, 1/4 cup white sugar, 1/4 tsp cinnamon, 3 tbsp butter cold
In a medium-sized bowl, add the flour, baking powder, baking soda, cinnamon, and salt. Mix together and set aside.
2 cups all purpose flour, 2 tsps baking powder, 1 tsp baking soda, 3/4 tsps cinnamon, 1/2 teaspoon salt
In a large bowl, add oil, eggs, sour cream, vanilla, and white sugar. Whisk together until combined and smooth.
1 cup white sugar, 1/2 cup oil, 2 large eggs, 1 tbsp vanilla, 1 cup sour cream
Add in the dry ingredients and using a spatula, slowly fold until a soft muffin batter forms. Mix until JUST combined.
Add in the apples and mix in. Do not over-mix!
2 cups apples
Evenly divide the batter between the muffin liners.
Sprinkle streusel on top.
Bake the muffins at 375°F for 18-22 minutes for tulip liners. If using regular liners, they will be done at the 15-17 minute mark. The muffins are ready when they bounce back at touch or a toothpick inserted comes out clean.