Prepare the streusel: Whisk the flour, both sugars, cinnamon, and salt in a small bowl and toss together with a fork. Cut in the cold butter using a fork or your hands until the mixture resembles pea-sized crumbs. Place the streusel in the refrigerator while you make the batter.
Prepare the cake: In a large mixing bowl, whisk together flour, sugar, brown sugar, baking soda, salt, and spices. If necessary, mash any large lumps of brown sugar.
In a medium sized mixing bowl, combine the sourdough starter, egg, sour cream, oil, and vanilla. Mix together until everything is fully combined.
Add the wet ingredients to the dry ingredients and stir until just combined.
Pour the batter into prepared loaf pan. Top evenly with the streusel, pressing it down gently into the top of the bread so it sticks.
Bake for 45 to 55 minutes, or until a toothpick inserted in the center comes out clean.
Cool the bread in the pan on a wire rack for about 15 minutes, then remove it from the pan using the parchment paper as a sling and allow it to cool completely.
Serve & enjoy!
You can substitute 4 oz of flour (a scant cup) and 4 oz warm water (½ cup, 118g) for the 1 cup of unfed sourdough starter. If desired, increase salt to 1 teaspoon.You can substitute applesauce for the canola oil for a lighter bread.It's important to keep the streusel chilled. That keeps it from melting into the batter while the bread is baking.This cake keeps well on the counter for several days, or you can wrap it in plastic wrap and freeze for longer term storage.This cake also makes a great gift and ships well!Alternative sizes
One large loaf in a standard loaf pan and two mini loaves using mini loaf pans. Bake the large loaf for 35 to 40 minutes and the mini loaves for 25 to 30 minutes