In a medium saucepan, combine the diced Granny Smith apples, 1/3 cup of granulated sugar, 1/2 teaspoon of ground cinnamon, 2 tablespoons of cornstarch, and 2 teaspoons of water.

Cook over medium heat for about 5-6 minutes until the apples are softened and the mixture thickens. Remove from heat and let cool.

In a small bowl, mix together 1/2 cup of packed dark brown sugar and 1/2 teaspoon of cinnamon. Set aside for later.

Preheat your oven to 350°F (175°C). Grease a 9×13-inch pan with nonstick spray.

In a stand mixer fitted with a paddle attachment, beat together the unsalted butter and granulated sugar until light and fluffy (approximately 3 minutes).

Add the applesauce, vanilla extract, and eggs, mixing on medium speed until combined.

In a separate bowl, whisk together the all-purpose flour, baking powder, baking soda, kosher salt, and ground cinnamon.

Gradually add this dry mixture and Greek yogurt to the wet mix, alternating between the two until just combined. Be careful not to overmix.

Spread half of the cake batter evenly in the prepared pan.

Spoon the cooled apple mixture over this layer, spreading to cover.

Sprinkle two-thirds of the brown sugar-cinnamon mix on top of the apples.

Carefully add the remaining cake batter over the apple mixture and smooth it out.

Top with the rest of the brown sugar-cinnamon mix.

Bake for 35-40 minutes, or until a toothpick inserted into the center comes out clean. Cover with foil during the last 10 minutes if it browns too quickly.

In a medium bowl, whisk together the powdered sugar, whole milk, and vanilla extract until smooth.

Once the cake is done and still warm, poke 30 holes on the surface using a butter knife. Pour the glaze evenly over the cake and spread it to cover.

Let the glaze set for about 20 minutes before serving.