Scalloped Potato Casserole

Growing up I loved scalloped potatoes. Everytime my dad would make them, I would be in heaven! I actually had no concept of what was in them until recently, when I tried to make them, and had to ask around, thinking It was cheese, and things. But no, there is no cheese. And they're really easy to make... and I turned them into a casserole!

Scalloped Potato Casserole
Ingredients:
Sauce:
2 tbsp vegan margarine
1 tbsp cornstarch
1 tbsp rice flour
2 tbsp cold water
1/2 tsp salt
1/4 tsp pepper
1/2 tsp rosemary
1 1/4 cup non-dairy milk

Vegetables:
3 Largish potatoes, sliced thin
1 smallish onion, chopped
1/2 a yellow pepper, chopped
1 cup mushrooms, sliced
1 cup frozen peas

Directions:
Preheat the oven to 375.
In a pot, bring your margarine, milk, and spices to a boil.
In a small bowl, mix together the cornstarch, rice flour, and cold water. Slowly add to the mixture, whisking until thickened and smooth.
Line the bottom of a casserole dish (Mine wasn't very large, probably has about a 6 cup capacity) with a layer of sliced potatoes. Top with all the mushrooms, and 1/3 of the onions. Pour 1/4 of the sauce on top of it.
Add another layer of potatoes, and the yellow pepper, and 1/3 of the onions. Pour another 1/4 of the sauce.
Add a third layer of potatoes, the peas, and the rest of the onions, and then top with a final layer of potatoes. Pour the rest of the sauce on top of the casserole. Cover.
Bake for 30-45 minutes, until sauce is boiling and the potatoes are cooked through.
I added an optional crust, where you mix together some rice flour, salt, pepper, and margarine, and crumble on top, and then broil for about 5 minutes, until the crust is crispy. This is completely optional.