Preheat the oven to 350 degrees F (175 degrees C). Grease a 9x11-inch cake pan.

Combine flour, white sugar, brown sugar, butter, and baking soda in a bowl until crumbly. Transfer 1 cup of crumbs to a small bowl and set aside. Add buttermilk and cinnamon to remaining crumbs and mix until batter is just combined and moist. Pour batter into the prepared cake pan and sprinkle reserved crumbs on top.

Bake in the preheated oven until a toothpick inserted into the center comes out clean, 30 to 35 minutes.