Preheat oven to 350F. 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 knife
or mix with a fork until the mixture resembles coarse crumbs. Set
aside 1 cup of the flour mixture.
Mix the baking powder and baking soda into the remaining flour
mixture. Add the room temperature buttermilk, egg, and vanilla -
you may want to do this with a mixer. The batter is very, very thick.
Vigorously mix everything together until the batter is smooth, fluffy,
and resembles frosting - about 2 full minutes. 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 - 50-
58 minutes. Mine took 55 minutes. Allow to cool for 10 minutes,
then remove the sides of the springform pan and allow cake to cool
completely before serving (about 2 hours)