Preheat oven to 350°F (177°C). Generously spray a 9-inch springform pan* with cooking spray or grease with butter. Sprinkle the bottom of the pan with 1 Tablespoon of flour and tap out the excess.

Whisk the flour, sugar, and salt together in a large mixing bowl until combined. Cut in the butter in very small pieces using a pastry blender or mix with a fork until the mixture resembles coarse crumbs. Place 1 cup of the butter/flour mixture in the refrigerator until ready to use in step 4.

Using a handheld or stand mixer with a paddle attachment, mix the baking powder and baking soda into the remaining flour mixture. Add the room temperature buttermilk, egg, and vanilla and beat on medium speed until smooth. The batter is very thick. Spoon the batter into the prepared springform pan, smoothing the top.

Add the brown sugar and cinnamon to the reserved flour mixture. Toss with a fork until well blended. Sprinkle the crumbs over the batter, pressingly lightly so they stick.

Bake the cake until the center is firm and a toothpick inserted in the center comes out clean, about 45-55 minutes. Baking time varies, so begin checking at 45 minutes and don’t be alarmed if your cake takes longer. Mine usually takes the full 55 minutes.

Cool cake for 10 minutes before removing the sides of the springform pan. For neat slices and best flavor, cool cake completely at room temperature before serving.