I love, love, love potato gratin dishes, and I love creamed leeks. So I thought this would be a great combination to try, and it is. I make this dish for most holidays as a special treat. This is not something you would make on a regular basis because it is extremely rich and decadent. You can easily swap out whatever your favorite cheese might be or a blend of several. I usally stick with Parmesan, but this time I went with a blend of Parmesan and Romano. —ADRIENE
Cut off root end of leeks and the woody dark green tops and discard. Split leeks in half lengthwise with a knife. Cut leeks in thin half moon slices. Leeks are very dirty and the best way to wash them is to take a large bowl filled with warm water and soak the leeks in the water and swish around several times. The dirt will sink to the bottom and the leeks will rise to the top. Scoop out the clean leeks from the top and lay out on a towel to absorb excess water.
Get a pot going on the stove top on medium heat and put in 2 tbs. of butter. Saute the minced garlic until it starts to turn lightly golden.
Add the cleaned leeks to the pot and saute for about 10 minutes.
Now add 1 cup of heavy cream and cook on low-medium heat until leeks are soft and the cream is almost all reduced. Season with salt and pepper to taste. This should take around 15 minutes.
Take 1/2 tbs. butter and generously grease the bottom and sides of the baking dish you will be using for this. Pre-heat oven to 350 degrees.
Peel potatoes and slice with a sharp knife around 1/8" thick. If your knife skills are not that good you can also use a slicing device such as a mandeline. You will need to do this step rather quick to avoid browning of the potatoes. (I would not recommend soaking in water, you do not want to wash away any of the starch.)
Gather your sliced potatoes, shredded cheese, creamed leek mixture, and salt and pepper in front of you. Start by shingling out a layer of sliced potatoes on the bottom of the dish by slightly overlapping them. Season them generously with salt and pepper, then spread out a thin layer of the creamed leek mixture, then top with an even coating of shredded cheese. Keep repeating this process until you get to the last and final layer of potatoes on top. You do not want to top the final layer of potatoes with anything but salt and pepper at this point. Reserve enough cheese to top off the dish later on.
Pour in the remaining 1 1/2 cups of cream slowly on top of the potato dish until it is all absorbed to the bottom. Now place in the oven to bake. I would recommend putting the baking dish on a sheet pan in case you get any boil over of the cream.
Bake for around 1 1/2 hours. Test with a knife in the center and make sure that the knife goes in very easily to ensure the whole dish is completely cooked through. Now top the dish with the remaining shredded cheese and bake for another 15 minutes or until the cheese is light golden brown.
Let it rest for 15 minutes before cutting into it, you will get cleaner pieces this way. Enjoy!