- 1/2 cup (70g) all-purpose flour
- 1/2 cup old fashioned oats
- 1/2 cup (110g) packed light-brown sugar
- 1/2 tsp baking powder
- 1/4 tsp ground cinnamon
- 1/4 tsp salt
- 1/3 cup (76g) unsalted butter , diced into small cubes
- 2 lbs Granny Smith apples (at room temperature) peeled, cored and sliced thin (about 1/8-inch)
- 3 Tbsp (42g) unsalted butter , melted
- 2 Tbsp all-purpose flour
- 3 Tbsp water
- 1 Tbsp lemon juice
- 1/2 tsp vanilla extract
- 1/4 cup (55g) light-brown sugar
- 1/2 tsp ground cinnamon
- 1 pinch salt
- 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.
- In a mixing bowl whisk together 1/2 cup flour, the oats, 1/2 cup brown sugar, the baking powder, 1/4 tsp cinnamon and 1/4 tsp salt for 30 seconds.
- 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.
- 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.
- 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.
- Remove topping from refrigerator and sprinkle into crumbles evenly over top of apples.
- Bake in preheated oven until top is golden brown and apples are tender when pierced with a toothpick, about 35 minutes.
- Remove from oven and allow to rest 10 minutes before serving. Serve warm with vanilla ice cream and salted caramel sauce if desired.