Preheat the oven to 325°F. Peel the red and sweet potatoes and slice them into thin slices. Combine the potatoes, so each type is evenly distributed.
In a small pot over low heat, melt the butter. Add the flour, sea salt, and coconut milk. Bring to a simmer and let cook until thickened. Immediately take off the heat.
Place half the potatoes in a 9 x 13-inch pan. Top with half the onions and half the sauce. Repeat the layers. Bake uncovered for 2 hours or until you can stick a fork clear through the potatoes to the bottom of the casserole dish.
Recipe by Natural Living Family with Dr. Z & Mama Z at https://naturallivingfamily.com/genes-scalloped-potatoes/