Cook quartered cabbage and potato slices in salted boiling water over medium heat for 5 minutes.
Let cabbage cool. Then cut the core out of each wedge and cut in half lengthwise. Slice into ½ inch-wide ribbons (1 cm wide). Drain in a colander for 5 minutes.
Preheat oven to 375°F (190°C). Butter a sizeable baking dish and rub with a halved garlic clove.
Slice remaining garlic and combine with cabbage and potatoes.
Mix together milk, crème fraiche, salt and pepper. Add into cabbage and potatoes along with the cheeses and sage.
Place all ingredients into the baking dish.
Bake 75-90 minutes. During the first 45 minutes press the vegetables down every 10-15 minutes with the back of a large spoon.
Let rest 10-15 minutes before serving.