Preheat oven to 350 degrees
Combine all cheeses into a bowl
Melt butter in large skillet over medium-high heat.
Add the onion and cook until tender.
Add the garlic, salt, & pepper and cook for 30 seconds. Stirring.
Gradually pour in the whole milk.
Bring the milk to a simmer. Reduce heat and cook 3 minutes. Do not scald the milk.
Add in the ground nutmeg.
Butter or spray with a cooking spray the bottom of a 9x13 inch baking dish.
Layer half of the potato slices in the baking dish.
Pour 1/2 of the milk on top of the potatoes.
Add 1/2 of the cheese on top of the potatoes.
Top with the remaining half of the potatoes.
Add the rest of the milk.
Cover tightly with foil and bake for 45 minutes.
Uncover and add the rest of the cheeses.
Bake for another 45 minutes uncovered.
Remove from the oven and cool for 10 minutes.