For the crumb topping:
1/2 cup all-purpose flour
1/2 cup old-fashioned rolled oats
1/2 cup light brown sugar
1/2 teaspoon baking powder
1/4 teaspoon ground cinnamon
1/3 cup unsalted butter,cut into small pieces

For the Apple filling:
3-4 large Baking apples, peeled and thinly sliced
3 Tablespoons butter, melted
2 Tablespoons all-purpose flour
3 Tablespoons milk
1/2 teaspoon vanilla extract
1/4 cup light brown sugar
1/2 teaspoon ground cinnamon
dash of salt

Preheat oven to 375 degrees F.
For the topping:
In a medium size bowl combine the crumb topping ingredients with a fork or pastry blender until it resembles small crumbs. Refrigerate while you prepare the apple filling.
For the Apple Filling:
(I use a Johnny Apple Peeler to peel and slice the apples all at once. It makes the process a lot faster!)

In a small bowl, combine melted butter and flour until well blended. Add lemon juice, milk and vanilla and stir well. Stir in brown sugar, cinnamon, and salt.
Pour butter mixture over apples and toss to coat. Pour apple mixture into an 8x8-inch baking dish and spread into an even layer.
Sprinkle crumb topping evenly over the apples.
Bake for 30-35 minutes or until golden brown and top is set.
Remove from oven and allow to cool for at least 10 minutes before serving.