Preheat the oven to 350 degrees. Place the vegan buttery spread in a saucepan and melt over medium heat. Add the chopped onion and cook for about 5 minutes, until tender. Stir in the gluten free flour blend. Add half the milk and stir well. Add the salt and pepper and continue to stir. Add the rest of the milk and turn the heat to medium high. Cook while stirring constantly for a minute or two to allow the sauce to thicken. Add the salt, pepper, and chopped ham and stir again. Place the thinly sliced potatoes in a casserole dish. Pour the sauce over the top. Dot the two tablespoons of vegan buttery spread over the top. Cover the dish and bake at 350 degrees for 30 minutes. Remove the cover and continue to bake for one hour and 10 minutes. Let stand for about 15 minutes before serving.