1 recipe Nick's Quick Brioche (Yeast Bread section) or 2 sheets frozen puff pastry
2 pounds Yukon Gold or red potatoes, peeled, sliced and blanched
12 ounces fresh or lightly smoked ham in 1/4" slices
8 ounces mushrooms, trimmed, cleaned, sliced and sauteed
2 cups bechamel sauce:
Roux: 2 tablespoons butter; 3 tablespoons flour
2 -1/2 cups milk
sea salt and freshly ground white pepper to taste
1 egg yolk diluted with 1 teaspoon water, lightly salted
Brioche: Prepare the brioche, divide into two pieces, one slightly larger than the other. Roll out the larger piece into a circle or oval large enough to cover the bottom and sides of a small sheet pan, oval casserole, or round 10" baking dish.
Puff paste: Cut 2 sheets into rounds, one large enough to fill the bottom of the pan and come up and sides, the other slightly smaller, but larger than the bottom of the pan. Lay the larger one in the pan.
Preheat the oven to 400 degrees.
Steam or boil the potatoes in lightly salted water until they yield easily to a knife. Drain.
Saute the mushrooms in butter until they begin to brown. Remove to a bowl to cool.
Bechamel: Melt the butter, add flour and cook for 2 minutes over medium low heat whisking continuously. Meanwhile heat the milk.
Off the heat pour hot milk into the roux. Return to the heat and bring to a boil, stirring continuously. Cook until thickened to taste. Season with salt and white pepper. When cooled, stir in the mushrooms
Fill the pastry-lined mold with alternating layers of potato and ham slices. Lightly salt and pepper each layer as well. End with the cream sauce.
Roll out the remaining piece of brioche. Lift it over the filling seal the dough layers with a decorative crimp. Lightly brush the crust with egg yolk. Proceed in the same manner if using smaller round of cold puff pastry.
Bake until golden brown, 40 minutes.