• Preheat oven to 325°F. Line an 8×8-inch baking dish with aluminum foil, including up the sides, leaving extra hanging over the edges. Spray with nonstick cooking spray. Set aside.

Apples

• In a medium saucepan, over medium heat, melt butter. Add apples, brown sugar, cinnamon, and salt. Cook for 5-8 minutes, or until the apples have softened slightly. Set aside.

Topping

• To a medium bowl, add butter, sugars, cinnamon, and salt. Stir to combine.
• Add the flour and stir until the mixture is completely combined. Be careful not to overmix or it can become like a paste.

Cake

• To the bowl of a stand mixer fitted with paddle attachment, add flour, sugar, cinnamon, salt, and baking soda. Mix on low speed to combine.
• Add butter pieces one at a time, mixing until there are no visible butter pieces and it has a very fine crumb, about 1 minute.
• Add buttermilk, egg, egg yolk, and vanilla. Mix at medium speed until light and fluffy, about 1 minute, scraping the bowl as needed.

Assembly

• Pour batter evenly into the prepared pan, spreading with a spatula if needed.
• Top with apple mixture.
• Using your hands or a fork, break up the crumb topping into pieces. Spread the topping in an even layer on top of the apples.
• Bake for 55-60 minutes, or until crumbs are golden and a toothpick inserted into the center of the cake comes out with a few crumbs, but no wet batter.
• Let the cake cool in the pan on a wire rack for 30 minutes. Then, using the excess aluminum foil, lift the cake out of the pan to continue cooling.
• When ready to serve, drizzle with caramel topping.