Preheat oven to 350� F/175� C. Whisk together sugars, DIY Cinnamon-Vanilla Seasoning, and softened butter until combined, should look like wet sand. Whisk in eggs, vanilla, and milk. Stir in flour and baking powder. Pour into UltraPro 2-Qt./2 L Square Pan (or UltraPro 2-Qt./2L Casserole Pan) and spread until even with spatula.
Make the topping
Stir together melted butter, oats, flour, and brown sugar in a small bowl. Set aside. Assemble Grate Master with slicing cone. Place a small bowl underneath. Place apple quarters one at a time into the hopper and turn handle to slice. Repeat until apple is sliced. Toss with oat mixture and sprinkle onto the top of batter.
Bake and serve
Top with apple topping and bake for 40-50 minutes or until an inserted knife comes out clean.
