Vegetarian Shepherd's Pie W/Wild Mushrooms

I love mushrooms, so the idea of creating a whole pie out of them is fabulous for me! I have yet to try this recipe, but received it via an email from Whole Foods Market. I will update when I've tried it! This recipe is also gluten-free.

• Ready In: 1 hr 15 mins
• Serves: 10-12

Ingredients

• 1 (2 ounce) package  mixed  dried wild mushrooms
• 3  tablespoons olive oil
• 3  cups  sliced white button mushrooms
• 5  portabella mushrooms, stems removed, rinsed, cut in half, then sliced crosswise
• 4  cups  sliced baby portabella mushrooms
• 2  cups  sliced shiitake mushrooms, rinsed and dried, stems removed
• 3  shallots, peeled and chopped
• 3  carrots, peeled and chopped
• 6  celery ribs, peeled and chopped
• 2  bay leaves
• 1 (28 ounce) can crushed tomatoes
•  sea salt, to taste
•  ground pepper, to taste
• 5  cups  leftover mashed potatoes (made with butter and milk)
• 2  cups  grated cheddar cheese or 2  cups monterey jack cheese
• 2  tablespoons  grated parmesan cheese

Directions

1. Preheat oven to 300°F.
2. In a small pot, heat about 3 cups of water to a boil. Add dried mushrooms and remove from heat. Let sit for 30 minutes to rehydrate.
3. Meanwhile, in a large Dutch oven, heat olive oil over medium heat. Add all fresh mushrooms and cook for about 20 minutes, uncovered, stirring occasionally, until most of the liquid has evaporated. Add shallot, carrots and celery and continue cooking for another 5 minutes.
4. Strain the dried mushrooms, reserving the soaking liquid, and add the mushrooms to the pot. Strain the soaking liquid through a fine mesh strainer to remove any grit. Add strained liquid to the mushroom mixture. Stir in bay leaves, tomatoes and one cup of water. Season with salt and pepper. Continue cooking over low heat until carrots are soft, about 15 minutes. Remove from heat. Taste and adjust seasoning. The mushroom mix can be prepared up to two days ahead and refrigerated.
5. Spread the mushroom mix in the bottom of a 3-quart baking dish. Cover with the mashed potatoes and sprinkle with the cheddar cheese and then the Parmesan. Bake until cheese is melted and pie is heated through, about 45 minutes. Serve immediately.