In a small bowl, add granulated sugar and cinnamon; whisk to blend. Generously grease a 9-inch springform pan; add some flour and tap out the excess. Sprinkle the bottom with ¼ cup granulated sugar mixed with cinnamon; set aside.
Preheat oven to 350ºF.
In a medium bowl, combine granulated sugar, brown sugar and cinnamon; stir until well blended. Add flour and stir to combine. Add butter and break down using a pastry cutter until the mixture resembles crumbles.
In another medium bowl, add flour, salt, baking powder, and baking soda; whisk until well mixed.
In the bowl of a stand mixer with the paddle attachment, add granulated sugar and butter; process until creamy and fluffy. Add vanilla and then eggs, one at a time, mixing well between each addition. Add a third of the dry ingredients and half the buttermilk; process on low speed until just combined before adding another third of the dry ingredients and buttermilk; combine again on low speed. Add the remaining flour mixture and process once again on low speed.
Spoon half of the batter evenly into the prepared pan and sprinkle on half of the crumble evenly; press down gently on the streusel so it sticks to the batter. Pour in the rest of the batter and level it out. Transfer the remaining streusel into the refrigerator for 15 minutes.
Place pan on a baking sheet lined with a silicone mat and transfer to the preheated oven; bake for 70 minutes or until a cake tester inserted in the center of the cake comes out clean.
After 15 minutes, remove cake quickly and evenly spoon on the remaining streusel (that will prevent it from sinking). Return cake to the oven for the remaining baking time.
After 35 minutes, cover cake with foil to prevent the streusel from getting too dark.
Remove from the heat and let the cake cool off for 30 minutes before removing the springform and serving.