This is from Epicurious. I made it in advance to simplify things for tomorrow and of course I had to sample it. Excellent. Although I admit I didn't actually measure anything and I used fresh thyme in place of fresh rosemary because that's what I had on hand. Oh, and I just used oyster mushrooms since that's what I had.
36 1/3-inch-thick baguette slices
2 tablespoons olive oil
1/3 cup chopped shallots
2 1/4 cups chopped oyster mushrooms
2 1/4 cups chopped stemmed shiitake mushrooms (about 6 ounces)
1 1/4 cups chopped chanterelle mushrooms (about 4 ounces)
1 garlic clove, minced
1/4 cup whipping cream
1 teaspoon minced fresh rosemary
1/2 teaspoon grated lemon peel
1 cup grated Fontina cheese
1/2 cup freshly grated Parmesan cheese (about 1 3/4 ounces)
Preheat oven to 375°F. Arrange baguette slices on rimmed baking sheet. Toast in oven until golden, about 9 minutes. Cool. (Can be prepared 2 days ahead. Store in airtight container at room temperature.)
Heat oil in large skillet over medium-high heat. Add shallots; sauté 1 minute. Add all mushrooms; sauté until beginning to brown, about 6 minutes. Stir in garlic; sauté 1 minute. Remove from heat. Stir in cream, rosemary, and lemon peel. Season with salt and pepper. Cool. Mix in both cheeses. (Can be made 2 days ahead. Cover and refrigerate.)
Preheat broiler. Top each toast with about 1 tablespoon mushroom topping. Place on 2 rimmed baking sheets. Working in batches, broil until cheese is melted and begins to brown, watching closely to prevent burning, about 3 minutes. Transfer to serving platter. Serve warm.