Preheat your oven to 350 degrees.
Next, in a small bowl combine the crumble topping ingredients (sugar, brown sugar, and cinnamon). Set aside.
In a large mixing bowl combine the dry ingredients (flour, sugar, brown sugar, baking soda, salt, cinnamon, and nutmeg). Mix well with a large spoon.
Combine the wet ingredients (sourdough starter or discard, oil, egg, and vanilla). Mix with a hand mixer until well combined.
Line a muffin tin with liners. Fill each to ⅔rds way full. Do not overfill. Add the crumble on top of each muffin.
Bake for 20 to 25 minutes or until a toothpick comes out clean from the middle.
