Crumb Topping ▢1/3 cup sugar ▢1/3 cup brown sugar ▢3/4 tsp cinnamon ▢1/8 tsp salt ▢1/2 cup butter melted ▢1 3/4 cup cake flour Cake ▢1 1/4 cup cake flour ▢1/2 cup sugar ▢1/4 tsp baking soda ▢1/4 tsp salt ▢6 tbsp butter cut into pieces, softened but cool ▢1 egg ▢1 egg yolk ▢1 tsp vanilla extract ▢1/3 cup buttermilk ▢powdered sugar for dusting
Preparing the oven to 325 degrees, position a rack in the upper center. Preheat a square pan measuring 8 by 8 inches and line it with enough parchment paper to drape over the sides. Aside; set aside.
Combine the granulated sugar, brown sugar, cinnamon, salt, and flour in a whisk until a crumbly topping forms.
Apply the melted butter to the mixture and combine completely using a wooden spoon or rubber spatula. The mixture will be doughy and viscous. Aside; set aside.
Cake: Combine the flour, sugar, baking soda, and salt using a hand or stand mixer to a smooth consistency. While the mixer is set to low, gradually incorporate the butter pieces one by one.
About one to two minutes later, the mixture should resemble moist crumbs with no visible butter pieces remaining. Buttermilk, egg, yolk, and vanilla are added.
Preparing a pan, evenly distribute the batter inside. Place the crumble topping on top of the batter, separating any large pieces into smaller ones that are the size of peas. Beginning at the periphery, gradually approach the core.
Bake the cake for 35 to 40 minutes, or until a toothpick inserted into it emerges clear and devoid of any crumb. Allow cake to chill for a minimum of 30 minutes after baking.