Get all your ingredients ready. Peel and slice your potatoes. Slice them thin but not too thin. We like number 2 on the mandolin. Slice your onion on the mandolin as well, or thinly with a knife. Grate all your cheese and melt the butter.
Pre-heat your oven to 375 degrees.
Put together the dish. Put a layer of potatoes, then sweet potatoes, then yams down in the pan. Add a thin layer of the onions and sprinkle all generously with salt, pepper, garlic powder, and a quarter of the aged cheddar. Repeat until the potatoes, onions and cheese are all used up. Finish with a layer of potatoes.
Pour the melted butter over top of all the potatoes, pour the coconut milk over top as well. Finish with all the gruyere cheese.
Cover with a lid or foil and bake for 30 mins. Then take the lid or foil off and bake another 15 -20 mins or until the dish is bubbling and nicely browned on top. Take out of the oven and let it sit for 5 - 10 mins before serving.