1large or 2 small/medium Granny Smith applespeeled, cored, and chopped into small chunks (about 2 cups)
Preheat oven to 400ºF.
Spray the wells of a cupcake pan with non-stick spray or line with cupcake liners. Set aside.
In a small bowl, combine brown sugar, flour, oats, and ground cinnamon. Toss together with a fork.
Add your softened, cubed butter and work into sugar mixture with a fork or your fingers until pea-sized clumps form. Set aside.
In a large bowl, whisk together flour, ground cinnamon, allspice, nutmeg, ground cloves, salt, baking powder, and baking soda. Set aside.
In a medium bowl, whisk together eggs, oil, apple butter, and vanilla until smooth. Whisk in both sugars until no clumps remain.
Pour wet ingredients into dry ingredients and stir gently until just combined and no white flour streaks remain. Gently fold in chopped apples.
Spoon the batter into the prepared wells. Sprinkle oat streusel mixture evenly onto each of the mounds of batter, about 3/4 Tablespoon for each. Bake the muffins for 5 minutes, then, without opening the oven door, decrease the temperature to 350ºF and bake for an additional 15-16 minutes, or until a toothpick inserted in center comes out mostly clean. Allow to cool completely on a wire rack before slicing and serving. Leftovers can be kept covered at room temperature for 4 days or in the refrigerator up to 6 days. Muffins freeze well, up to 2 months. Thaw in refrigerator overnight or thaw in the microwave about 10 seconds.