First, wash and then slice the potatoes into uniformly thin pieces.
Next, make the sauce. Start by finely chopping the shallot and mincing the garlic.
In a pot or saucepan over medium heat, melt the butter. Cook the onion for 2 minutes then add the garlic and cook another minute.
Sprinkle the flour into the pot and stir; this will create a thick paste.
Slowly stir in the stock, creating a thin gravy consistency. Then slowly stir in the milk. Season with salt and pepper.
Prepare a 9×13 casserole pan by spraying with nonstick cooking spray or greasing with a little butter.
Layer in half of the potato slices. Cover with half of the sauce. Sprinkle on half the cheese (both cheeses). Then layer on the rest of the potatoes and pour the remaining sauce over these. Top with the remainder of the cheeses. Last, sprinkle on some fresh herbs—chives, thyme or rosemary or a combination.
Cover the dish in aluminum foil and bake at 400°F for 30 minutes.
Remove the foil and bake for an additional 30 minutes.