Preheat the oven to 375℉. Spray a 9-inch pie plate with nonstick spray (or rub with butter).
Add the apples to the pie plate. Sprinkle the lemon juice evenly over the apples.
In a medium bowl, whisk together the flour, sugars, cinnamon, nutmeg and salt. Use a pastry blender (or two knives) to cut the butter into the flour mixture (you're looking for the consistency of coarse crumbs). Sprinkle the flour mixture evenly over the apples.
Bake for 30 minutes. Cover the top of the apple betty with a piece of foil (to avoid excessive browning), and bake for an additional 15 to 20 minutes.
Great served with vanilla ice cream!
Notes
If you want to add 2 tablespoons of oats to your topping, that's completely up to you. It's not traditional for an Apple Brown Betty, but some people like oats in the topping!