A really good "gratin" is such European comfort food... it's kind of like Mac and Cheese, to me, but fancier so you could serve it up with a nice cut of meat, and there it would make for a really festive meal. But it's also so easy to do.
I put together this little casserole a few days ago, but didn't have time to write up the description. So without further ado, here it is, in all its beautiful simplicity!
2 cups of 'fingerling' potatoes, or Baby Dutch yellow, or Yukons, sliced into 1/4" thick discs
2 leeks, sliced into 1/4" discs
2 cups heavy cream (!)
2 tbsp Dijon mustard
2-3 cloves of garlic (to your preference), minced
1 tsp salt
1/2 tsp ground white pepper
1/2 cup grated Gouda cheese
Preheat oven to 400-415. Slice and layer ingredients in a large glass baking dish. The shape is of no consequence.
In a mixing bowl or measuring cup, whisk together mustard, cream, and minced garlic plus salt and pepper.
Pour cream over all potatoes and leeks, and make sure they're submerged. If necessary, dilute with a little water or milk. (For that matter, you could use half-n-half, or if you feel industrious, make a whole milk roux [see my Macaroni and cheeeeeeeeese!!!! recipe for instructions on Roux] if you want less fat. But really, I kind of go nuts with the heavy cream when it comes to Au Gratin.)
Sprinkle grated cheese on top.
Bake with aluminum foil covering the dish for about 20 minutes, and then remove foil to allow to brown.
The au gratin is done when the potatoes are fork tender, and the top is browned a bit and bubbly in the middle.