Step 1

Preheat oven to 375 degrees and position oven rack one level below the center. Butter an 8 by 8 inch baking dish (or small casserole dish with a similar size), set aside.

Step 2

In a mixing bowl whisk together 1/2 cup flour, the oats, 1/2 cup brown sugar, 1/2 tsp baking powder, 1/4 tsp cinnamon and 1/4 tsp salt for 30 seconds.

Step 3

Add diced butter and using clean fingertips, rub butter into dry mixture until it comes together into small crumbles. Transfer to refrigerator to chill while preparing filling.

Step 4

In a small mixing bowl, whisk together melted butter and flour until well blended, then mix in water, lemon juice and vanilla. Stir in 1/4 cup brown sugar, 1/2 tsp cinnamon, and pinch of salt.

Step 5

Place apples in a large bowl then pour butter mixture over apples and toss to evenly coat, then pour apple mixture into prepared baking dish and spread into an even layer.

Step 6

Remove topping from refrigerator and sprinkle into crumbles evenly over top of apples.

Step 7

Bake in preheated oven until top is golden brown and apples are tender when pierced with a toothpick, about 35 minutes.

Step 8

Remove from oven and allow to rest 10 minutes before serving. Serve warm with vanilla ice cream and salted caramel sauce if desired.