Scalloped Potatoes with Leeks and Slow-Cooked Onions

Makes a 9" x 13" pan
This recipe is from Palisades; the measurements are approximate (like making a lasagna). It's important to blanch the potatoes as a first step. Best if made a day ahead.

Ingredients:
2 pounds of russet potatoes, peeled, blanched and sliced 1/4 inch thick
Parmesan cheese - one cup, grated
Gouda cheese - one cup, grated
black pepper
sea or kosher salt

Leek/onion mix:
2 T. olive oil
1 large sweet onion, peeled and thinly sliced
2 cloves garlic, minced
3 medium leeks, washed, trimmed, and thinly sliced
1/4 cup dry white wine
1/2 tsp. ground thyme

White sauce:
2 T. butter
2 T. flour
1/2 tsp. salt
1/4 tsp. ground pepper
1 cup vegetable broth
1 bay leaf
1/4 cup sour cream
1/2 cup whipping cream

Heat olive oil in large frying pan. Add the onion, garlic and leeks. Saute until the mix begins to caramelize, Add thyme, reduce heat to low and let onion mixture cook and mature until tender.
De-glaze with white wine and reduce until mixture is almost dry.

To make the white sauce, begin by melting the butter in a sauce pan. Whisk in the flour, creating a roux. Cook without scorching for 3-4 minutes. Add the broth, whip cream and bay leaf. Whisk to blend, and cook until sauce is smooth. Turn off heat and blend in the sour cream and salt. Remove bay leaf before assembling the dish.

To assemble:
Preheat the oven to 400 degrees

Evenly layer half the potatoes in buttered pan. Season with a sprinkle of salt and pepper.

Layer half of the onion-leek mixture on top of the potatoes

Mix grated parmesan and gouda together, and scatter half on top of the onion mixture

Layer the rest of the potatoes evenly into the pan. Season with the remaining salt and pepper.

Top with the rest of the onion/leek mixture

Pour the sour cream sauce over the potoatoes (you don't need to use all of it if the pan seems to full). Sprinkle the rest of the cheese on top.

Cover the pan with foil and cut a couple of vent slits in the foil.

Bake for 45-50 minutes, then remove foil and bake another ten minutes.

If making ahead, cool, refrigerate and re-heat for 25 minutes until heated through.