6-7 medium yukon gold potatoes, thinly sliced into 1/8th inch rounds (3 pounds gold potatoes -- by weight is a more accurate measure)
½ white or yellow onion, cut into slices
For the sauce:
2 tablespoons salted butter
¼ cup all purpose flour (whole wheat, all purpose, or gluten free 1:1 flour will all work)
1 1/2 cups unsweetened almond milk (regular, skim or whole milk will also work)
8 ounces sharp cheddar cheese (2 heaping cups shredded cheddar cheese)
½ teaspoon garlic powder
¾ teaspoon salt, plus more to taste
Freshly ground black pepper

For topping:
1/2 cup gruyere cheese (or sub more sharp cheddar)
¼ cup grated parmesan

To garnish:
Fresh chopped parsley