Preheat your oven to 350 degrees and grease a 9 inch baking dish.
In a large mixing bowl combine your dry ingredients (flour, sugar, brown sugar, baking soda, salt, cinnamon, and nutmeg). Stir well with a large spoon.
1 cup all purpose flour, ½ cup sugar, ¼ cup brown sugar, ½ teaspoon salt, 1 teaspoon baking soda, 1 teaspoon cinnamon, ¼ teaspoon nutmeg
Next, add in your wet ingredients and mix well with a hand mixer.
1 cup sourdough starter, ⅓ cup vegetable oil, 1 large egg, 1 teaspoon vanilla extract
Pour the batter into the baking dish. Stir in nuts (these are optional).
⅓ cup pecans or walnuts
Next, in a medium bowl combine the ingredients for the topping (brown sugar, butter, cinnamon, and flour). Use a pastry cutter or two forks to combine and press into the ingredients until the topping is pea sized.
⅓ cup brown sugar, ¾ teaspoon cinnamon, 3 tablespoons butter, 1 ½ tablespoons all purpose flour
Sprinkle the topping over the batter and bake for 30 to 35 minutes or until a toothpick comes out clean from the middle of the cake.