Potato and Fennel gratin

Peel and slice 10 potatoes, 1 yellow onion and 2 fennel bulbs with a "mandoline" and layer them in an oven-safe dish. Mix together 3 dl cream, 2 dl milk (or just use 5 dl of light cream), a crushed garlic head and thyme, and pour it into the form, pressing down to see that it just covers the potato mix. Top with shredded cheese 9and in this case think slices of dry goat cheese, because I had some left over) and bake at 220 C / 430 F for 40-45 minutes.