Preheat the oven to 400°F or 205 Celsius

Rub the inside of a baking dish with 1/2 tablespoon of butter.

Smash the garlic with the side of a knife. Dice it and sprinkle with salt. Finely chop and mix until you have a paste

Combine half and half, garlic, potatoes and remaining butter in a pot. Bring to a boil over medium high heat.

Cook for 10 minutes stirring constantly. Be careful not to break the potato slices. The potato starch will have thicken the sauce.

Transfer in the dish and smooth out the top.

Hold until ready to bake (or refrigerate overnight).

Or cover with Gruyere and cook for 20 to 30 minutes until you have a nice golden brown crust.