To make your topping:

In a medium bowl, whisk together the flour, sugar, salt, cinnamon, allspice, and nutmeg. Add oatmeal and toss in the pieces of butter and, using your fingertips, squash it into the dry ingredients until small clumps the size of peas form. Don’t worry about having uniform sizes, just be sure the butter is evenly dispersed. Cover and refrigerate until ready to use. This step can be done a day ahead.

Now make your filling:
Preheat the oven to 375º and have an 9 x 13 x2 inch (ungreased) glass baking dish ready to go.

Place the sugar and butter into a large skillet and stir over medium heat until a smooth sauce forms. Add the lemon juice and continue to cook, stirring until the caramel is a medium to deep brown. It will take 5-8 minutes but mine took a little longer. Keep your eyes on it, you want the caramel color. You will be baking this too so don’t burn the caramel. Set a little aside for drizzling. Combine salt and diced apples and put them into the skillet with your caramel mixture. Toss until they are evenly coated with caramel. Pour apples and caramel into the baking dish. Spread them around in an even layer. Sprinkle with the chilled topping.

Bake for about 50 minutes or until the apples are tender (test carefully by piercing with a fork). The sauce will thicken and the topping should be golden. Remove from oven and place on a wire rack. Wait at least 30 minutes before serving. Serve it with ice cream and drizzle with caramel sauce.