Preheat oven to 375 degrees.
For the topping: In a medium size bowl, using a fork or pastry blender, combine the ingredients for the crumb topping until it resembles small crumbs. Refrigerate while preparing the apple filling.
For the apple filling: In a small bowl, combine melted butter and flour until well blended. Add lemon juice, milk and vanilla, stirring well. Stir in the brown sugar, cinnamon and salt.
Pour batter mixture over apples and toss to coat. Pour apple mixture into an 8×8 inch baking dish and spread evenly. Sprinkle crumb topping evenly over apples.
Bake for 30 to 35 minutes or until golden brown and top is set. Remove from oven and allow to cool for at least 10 minutes before serving.
Optional: Serve with vanilla ice cream or caramel sauce.