1/4 cup salted butter, cold and cut into small pieces
Instructions
Preheat the oven to 350 degrees Fahrenheit. Add 12 muffin cups to a muffin tin.
In a medium bowl, mix the 1 1/2 cups all-purpose flour, 1/2 cup rolled oats, and 2 teaspoons cinnamon with the ginger, allspice, baking powder, baking soda, and kosher salt.
In another bowl, combine the maple syrup, applesauce, unsalted butter (melted), and vanilla.
Mix the wet ingredients into the dry ingredients and stir until a smooth batter forms. Mix in the diced apple.
In another medium bowl, add the remaining 1/4 cup rolled oats, 2 tablespoons flour, and 1 teaspoon cinnamon along with the turbinado sugar and salted butter (cut into small pieces). Cut the butter into the remaining ingredients using a pastry cutter or fork until it’s evenly combined and a crumbly streusel topping forms.
Divide the batter evenly into the muffin cups. Then top with a thin layer of streusel.
Bake for about 25 to 30 minutes, until a toothpick comes out clean (if your oven is uneven, reverse the pan halfway through). Allow to cool in the pan for 5 minutes, then remove the muffins and place them on a cooling rack to fully cool.