1/2cup(1 stick) unsalted butter softened to room temperature
1/2cuppacked brown sugar
2large bananas (or 3 medium)mashed
In a medium bowl, whisk together the flour, both sugars, and salt until thoroughly combined. Drizzle melted butter over the flour mixture.
Stir with a spatula until a fine, sandy crumb forms. You may also use your hands to break up larger chunks. Set aside.
Preheat the oven to 350ºF. Spray a 9" x 13" baking sheet with non-stick spray. Set aside.
In a medium bowl, whisk together the flour, baking soda, cinnamon, and salt. Set aside.
Whisk the buttermilk and vanilla together in a small bowl or measuring cup. Set aside.
In a large bowl with a handheld mixer or the bowl of a stand mixer fitted with the paddle attachment, cream together the butter and both sugars on medium-high speed until light and fluffy (about 2-3 minutes). Beat the eggs in one at a time until fully incorporated, scraping down the sides and bottom of the bowl as necessary.
Reduce mixer speed to medium and add half of the flour mixture to the batter, followed by half of the buttermilk mixture. Beat until incorporated. Repeat with remaining flour and buttermilk mixtures. Fold in the mashed bananas with a spatula until just combined.
Pour the batter into the prepared baking dish, making sure to spread the batter evenly. Top with sandy crumbs, ensuring even distribution again. Bake the cake for 20-22 minutes until golden brown and a toothpick inserted into the middle comes out clean. Remove from the oven and allow to cool completely on a wire rack before serving.