GRATIN OF POTATOES, MUSHROOMS AND TOMATOES

1 1/2 cups hot water
3/4 oz dried porcini mushrooms
4 tb olive oil
8 oz fresh Portobello mushrooms, cleaned, trimmed and sliced
1 1/2 tsp salt
2 medium potatoes, pared and sliced
ground pepper to taste
2 medium tomatoes, sliced
1/4 cup grated sharp Provolone cheese
1/4 cup grated mozzarella

Pour hot water over Porcini and soak 30 minutes. Drain Porcini; strain the liquid and measure 2/3 cup of it for the recipe. Rinse Porcini under warm water; squeeze dry and chop fine. Reserve Porcini and 2/3 cup soaking liquid separately. Heat 2 Tb of the Olive oil in heavy medium skillet over high heat. Add Portobellos and 1/4 tsp salt. Sauté until golden and soft. Remove from heat. Heat oven to 400F. Brush a 10 inch gratin dish with 1 tb olive oil. Arrange potatoes in a layer over bottom of the dish; add the 2/3 cup soaking liquid, 1 tsp salt and pepper to taste. Scatter the Portobellos and Porcini over the potatoes; arrange tomatoes in a layer over mushrooms. Sprinkle with remaining 1/4 tsp salt and more pepper to taste; drizzle remaining 1 tb oil over all. Bake until potatoes are just tender, 20 to 25 minutes. Remove gratin dish from oven. Combine provolone and mozzarella; sprinkle on top of tomatoes. Bake until cheese is melted and forms a golden crust, about 10 minutes. Remove from oven and let stand for at least 15 minutes before serving.