In a medium saucepan over medium heat, combine the diced Granny Smith apples, white sugar, cornstarch, ground cinnamon, and a splash of water. Stir frequently for 5–7 minutes until the apples soften and release their juices.

In a small bowl, mix together the ground cinnamon and white sugar for the cinnamon sugar layer. Set this mixture aside.

Preheat your oven to 350°F (175°C) and generously grease a 9x13-inch baking pan.

In a large mixing bowl, cream the unsalted butter with white sugar on medium speed until light and fluffy, about 3–5 minutes.

Add the applesauce, vanilla extract, and room temperature eggs to the creamed butter mixture and mix until smooth.

In a separate bowl, whisk together the all-purpose flour, baking powder, baking soda, kosher salt, and additional cinnamon. Gradually add these dry ingredients to the wet mixture, alternating with the Greek yogurt.

Spread half of the batter evenly in the prepared baking pan. Spoon the cooked apple filling over the batter, then sprinkle half of the cinnamon sugar mixture on top. Add the remaining batter, followed by the leftover cinnamon sugar.

Bake for 35–40 minutes, checking for doneness by inserting a toothpick into the center.

While the cake is baking, whisk together the powdered sugar, milk, and vanilla extract until smooth.

Once the cake is baked and has cooled for about 10–15 minutes, poke holes in the surface. Pour the glaze evenly over the warm cake.