Preheat the oven to 325F. Spray a round 8-inch cake pan (with at least 2-inch sides) with baking spray. Line the bottom of the pan with a circle of parchment paper. (If your pan does not have 2 inch sides, use a 9-inch round pan.)
Sprinkle the baking soda, baking powder, salt and cinnamon over the top and stir to combine. Add the flour and stir just until all of the flour is incorporated.
Transfer the batter to the prepared pan and bake for 20 minutes. Carefully remove the pan from the oven and gently top with the crumb topping.
Return the pan to the oven and bake for another 18-25 minutes(a total time of 38-45 minutes), until the center is firm when touched lightly on the top of the cake. You can also test the doneness with a toothpick inserted into the center of the cake. It will come out clean or with just a few crumbs when the cake is done. You can also test the doneness with an instant thermometer which should register 205-210˚F when the cake is finished.
Allow the cake to cool for 10 minutes then invert onto a clean plate. Invert again onto a cooling rack so that the crumb topping is back on the top. Allow the cake to cool for 15-20 minutes before adding the drizzle.
Combine powdered sugar, milk (or half and half) and vanilla and stir well with a small whisk or a fork. Drizzle over the top of the cake and ENJOY!