Buttery Coffee Cake

In a medium bowl, mix together the flour, cornstarch, brown sugar, sugar, and cinnamon (add a pinch of kosher salt if using unsalted butter).

Pour in the butter and mix, ensuring all of the crumble is evenly hydrated with no patchy dry spots. It should be very thick and clumpy.

Place the bowl in the refrigerator while we make the cake batter.

Preheat the oven to 350F and grease and line an 8×8 pan with parchment paper. Allow the paper to reach up and over the sides for easy removal once the cake is baked.

In a large bowl, use a fork to mash and mix together the butter, oil, and sugar. Once combined, switch to a whisk and thoroughly mix until creamy and lightened in color. Now whisk in the egg, egg yolk, vanilla, and sour cream. Once smooth, whisk in the baking soda, baking powder, and salt to distribute. Last, whisk in the flour until you reach a creamy cake batter.

Spread the batter into the prepared pan. Remove the crumble from the refrigerator – it should be nearly solidified together so use your hands to break it up into a fine crumb. Sprinkle a thick and even layer over the batter.

Bake for 30 to 35 minutes or until the cake has an even rise and the center doesn’t move when the pan is nudged.

Allow the cake to cool for about an hour, then release it from the pan, top with a dusting of powdered sugar, slice, and enjoy!