Work quickly with the potatoes as they tend to turn brown once they are grated.
Grate the potatoes either with a grater or in the food processor; squeeze them with your hands to remove excess water if they seem at all wet.
Mix them with the garlic and season with salt and pepper. Gently heat the oil and butter in a large frying-pan
Turn up the heat under the pan for a moment then put in the grated potato and garlic and press it down into a kind of thin straw mat.
Cook over a low heat for 10–15 minutes, making sure it does not stick or burn. Flip the mat over or turn like a tortilla, by using a large flat plate, and cook the second side for a further 10–15 minutes.
Cut it like a cake and serve with confit and green salad, dressed with olive or nut oil and lemon juice.