Harvest Scalloped Potatoes

6-8 medium sized all-purpose potatoes (Yukon Golds are perfect)
1 medium onion
3-4 cloves garlic, whole
pint heavy cream
pint half and half
1 tsp Dijon mustard (or 1 tsp horseradish)
1 tsp salt
1/2 tsp pepper
1-1 1/2 cups grated cheese (Gruyere, white cheddar, Parmesan or a mixture of all 3)

Peel potatoes and slice into 5 mm (1/4 inch) rounds. Slice onion into crescents.
Put potatoes, whole garlic and onion in a large heavy-bottomed pot and add equal amounts of the cream to not quite cover the sliced potatoes.
Add the mustard or horseradish, salt and pepper, and mix.
Cook over medium heat, adding half the grated cheese part way through, stirring carefully, until the potatoes are partially cooked but still firm and cooked enough to be pierced with a knife.
Slide everything into a baking dish and top with the rest of the cheese (I leave the garlic in; it becomes soft and sweet but remove it if you like).
Bake at 175 C (350 F) for about 30 minutes or until bubbling and golden.
Let cool for 10 minutes before serving.

Use cream instead of milk. It's richer and won't split while cooking.