Crust
1 cup unsalted butter
1/2 tsp vanilla extract
3/4 cup brown sugar
3 cups flour
1/2 tsp salt
Filling
3 Tbsp unsalted butter
1/4 cup brown sugar
8 cups Fuji apples, peeled, cored, and sliced into diamonds
1 Tbsp cinnamon
1/4 tsp nutmeg
1 cup water, as needed
Topping
2 cups rolled oats
1 cup flour
3/4 cup brown sugar
1 1/4 tsp cinnamon
1/2 tsp baking soda
1/2 tsp salt
1/2 tsp vanilla extract
5 Tbsp unsalted butter, melted