• Preheat the oven to 350℉/176℃. Line a 9x9 baking tray with parchment paper and set aside. Chop the apples into small cubes and set aside.
  2 cups apples

For the cake

• In a bowl, add the flour, baking soda, baking powder, cornstarch, and salt. Stir together and set aside.
  1 3/4 cups all-purpose flour, 3/4 tsp baking powder, 3/4 tsp baking soda, 1 tbsp cornstarch, 1/4 tsp salt
• In a large bowl, add the white sugar and oil. Whisk vigorously for 2-3 minutes until smooth.
  2/3 cups white sugar, 2/3 cups oil
• Add in the eggs and vanilla, and continue whisking.
  2 eggs, 1 tbsp vanilla
• Add in the sour cream, and whisk together, scraping the bowl as needed.
  2/3 cups sour cream
• Combine the wet and dry ingredients together with a spatula just until a soft cake batter forms, do not over-mix.
• Add in the chopped apples and once again, mix together just until evenly distributed. Don't over-mix!
  2 cups apples

For the cinnamon filling

• Add together the brown sugar, cinnamon, and melted butter. Stir together until a filling forms.
  1/2 cup dark brown sugar, 6 tbsp butter*, 2 tsp cinnamon

Layering

• Transfer the cake batter into the prepared pan and spread evenly. Take the cinnamon filling and dollop it all around the cake, then swirl it in with a knife.
• Bake the cake for 45-60 minutes or until a toothpick inserted in the middle comes out clean.
• Once baked, make the glaze. Combine powdered sugar with milk (or lemon juice if you want a tart glaze). Start with 1 tbsp of liquid, then add more depending on the consistency you want. Drizzle it on the cake, allow it to set, then slice and enjoy!
  1 cup powdered sugar, 1-2 tbsp milk