Cut Potato (3) into planks, blanch in salted water, drain, shock in ice water.
Grate Cheddar Cheese (1 cup) and Parmigiano-Reggiano (1 cup) and set aside.
Cut Italian Sausage (5) into small pieces; no need to remove the skin.
Saute sausages in Garlic Oil (to taste) until cooked.
Coat a baking dish with Garlic Paste (to taste) and Garlic Oil (to taste)
Sprinkle with grated Parmesan Cheese (to taste) and some of the sliced Onion (1).
Pour on some of the Tomato Sauce (1 cup).
Top with a layer of potatoes. Sprinkle with parmesan.
Add more sliced onions, grated cheddar and half of the sausages.
Drizzle with more tomato sauce and sprinkle with Italian Flat-Leaf Parsley (to taste).
Add another layer of sausage, sauce, cheddar and parmesan.
Add Milk (1 cup) that has been seasoned with Kosher Salt (to taste) and Cayenne Pepper (to taste). Bake at 320 degrees F (160 degrees C) for 1 hour.
To serve at once, scoop out with a serving spoon, otherwise, let slightly cool and set, then cut with a knife and serve with a spatula.