Preheat the oven to 350°F. On the stove top, place the potatoes, salt and garlic in a large pot and cover with water. Bring to a boil then reduce the heat to medium and cook for 8 to 10 minutes.
Drain the potatoes and place half in a buttered dish. Heat the cream and milk on the stove top or microwave until just warm.
Cover the potatoes with 1/2 cup cream mixture, a half cup of the cheddar cheese and one cup of the Gruyere cheese and sprinkle with salt, pepper and nutmeg.
Then add the rest of the potatoes to the dish, the remaining 1/2 cup cream mixture, sprinkle with pepper and nutmeg. Finally add the rest of cheddar and Gruyere cheese.
Bake the dish for one hour or until the cheese is bubbly and brown on top.