Preheat oven to 350°F. Spray 9-inch pan with cooking spray or grease with butter. Sprinkle bottom of pan with 1 tbps flour.

Whisk the flour, sugar, and salt together in a large mixing bowl until combined. Cut the butter into very small pieces, toss into mixture and mix it all up until the mixture resembles small crumbs. Set aside 1 cup of the mixture.

Mix the baking powder and baking soda into the remaining flour mixture. Add the room temperature buttermilk, egg, and vanilla. Vigorously mix everything together until the batter is smooth, fluffy, and resembles frosting. Spoon the batter into the prepared pan, smoothing the top.

Add the brown sugar and cinnamon to the reserved flour mixture and mix all together. Sprinkle crumbs over batter, pressing lightly so they stick. Bake the cake until the center is firm and a toothpick inserted comes out clean. 50-58 mins. Allow to cool for 10 mins.