Step 1Heat the oven to 375 degrees. Whisk together the cream, eggs, 1 teaspoon salt and one-half teaspoon black pepper and set aside.
Step 2Roast the mushrooms with one-half teaspoon salt, one-fourth teaspoon pepper, the garlic and olive oil until they are tender and have released their water (25 to 40 minutes, depending on the size of the mushrooms). Cool, then slice the mushrooms.
Step 3Place the mushroom mixture, cheese, bread and thyme into a large mixing bowl. Add the egg mixture and incorporate.
Step 4Transfer the mixture into a 13-by-9-inch baking dish and let stand 15 minutes, pressing down with a wooden spoon occasionally so the bread is submerged. Dot with truffle butter or salted butter and bake for about 35 minutes, or until a knife inserted into the center comes out clean.