Solar oven Escalloped Potatoes - from food storage items

Cooking homemade scalloped potatoes from storage foods - cooking it in the solar oven too.

2 cups dehydrated potato slices
1 small can cooked ham
3 tbs butter (or any oil)

3 tbs all purpose flour
1 can condensed milk (not sweetened condensed milk) with enough water to make 2 cups
---- or 2 cups prepared powdered milk
1 cup grated Parmesan
3 Tbs dried onions
1/2 teaspoon white pepper
-- I added 1/2 tsp dry mustard powder
In a saucepan over medium heat, melt the butter. Add flour, whisking well and consistently until a golden brown roux forms, about 3 minutes. Add milk slowly, whisking vigorously until well incorporated. Reduce heat off and add Parmesan cheese. Whisk slowly and frequently until sauce is smooth and rich, about 5 minutes. Add pepper and other spices as desired. Taste. If needed, add more salt and pepper (Note: sauce should be somewhat salty, as the potatoes will dilute the saltiness considerably when baking.)
In a greased glass casserole dish, line the potatoes on the bottom, overlapping them slightly. Pour a generous layer of the Béchamel sauce over the potatoes and scatter a handful of the canned ham. Continue in 1 or 2 more layers, reserving enough béchamel to cover the top.

 I just use the solar oven all day with the casserole dish covered tightly with a lid or plastic wrap - nope, never had it melt. (Knew you were going to ask.)