Preheat oven to 350 degrees and grease and flour a 9-inch springform pan or a 9-inch cake pan. You could also use baking spray to prep the cake pan. Set aside.
CRUMB TOPPING
In a bowl, combine flour, salt, cinnamon, and brown sugar. Cut in butter with a pastry cutter, and mix until the topping looks like coarse crumbs. Set aside.
CAKE
In a large bowl, mix the flour, baking powder, baking soda, the spies and salt.
In a separate bowl, whisk pumpkin and brown sugar together until combined. Add in oil, eggs, and vanilla extract. Mix until well combined. Add the sourdough starter and mix again.
Add the dry ingredients to the wet ingredients, and stir until all ingredients are well incorporated.
Pour the batter into the pan. Spread the crumb topping evenly over the batter.
Bake for 45-50 minutes, or until a cake tester comes out clean. Let cool a bit before removing cake from baking pan to your dish.
GLAZE
Once cake is cooled, whisk together the remaining milk and the powdered sugar. If you need your glaze to be thicker, add more powdered sugar. If you like it thinner, adjust with more milk. Drizzle glaze on top of the streusel. Enjoy!