Preheat the oven to 350 degrees F.
In a small bowl, mix together the flour, baking powder, and baking soda. Set that aside.
In the bowl of your stand mixer fitted with the paddle attachment, add the butter and sugar. Mix well. Then add the three eggs and the vanilla extract. Mix again.
Add in the sourdough discard and sour cream. Give it one more mix. Then add the dry ingredients to the bowl of the stand mixer. Mix on low speed for about 1 minute until all the ingredients are mixed together. There might be a few lumps but that is ok. Don't overmix here.
In a separate small bowl, mix together the flour, brown sugar, and cinnamon. Mix well.
In another medium bowl, mix together all of the crumb ingredients until it looks like large clumps of sand. Set that aside.
Butter a 9x13 inch baking dish. Add half the cake mixture to the bottom of the pan. Add the cinnamon sugar filling and spread it all out. Top it with the rest of the cake mix and then the crumb.
Bake for 45 minutes or until a toothpick is inserted and comes out clean. Let it cool slightly before serving.