03Line the baking dish with a crisscrossed layer of country ham, then a layer of slightly overlapping potatoes, then about 2/3 cup sauce. Repeat the layering until all the ingredients are used. You should have a total of 3 sets of layers, ending with the sauce on top. Top with the Gruyere and cover with foil. Bake until the potatoes are tender, about 1 hour.04Remove the foil and spoon off any fat that has pooled in the baking dish, if needed. Switch the oven to broil and broil until light golden brown, 3 to 5 minutes. Garnish with green onions before serving.