Preheat the oven to 375°F. Butter a 9 by 13-inch baking dish.
Fill a large pot halfway full of water, and add 2 tablespoons kosher salt, and bring to a boil over high heat.
Add the pasta, stir, and let cook until al dente, about 8 minutes or according to package directions. Reserve 1/4 cup pasta water.
In a large frying pan over medium-low heat, warm the olive oil.
Add the sliced shallots and a pinch of kosher salt and cook for 3 minutes, until starting to turn translucent.
Add the mushrooms and another pinch of kosher salt and cook, stirring, for about 5 minutes, or until the mushrooms are just starting to become tender and release their liquid.
Add the sherry, thyme, and black pepper and continue to cook until the mushrooms are just tender, 2 or 3 minutes longer.
In a large mixing bowl, stir together half of the gruyere, the crème fraiche, and the yogurt. Add the mushroom mixture and stir to combine, then stir in the pasta.
Season to taste with Morton Kosher Salt. Spread in the prepared baking dish and sprinkle with the remaining gruyere, topping with thyme sprigs.
Bake until golden brown and bubbly, about 30 minutes. Serve at once.
- 2 tablespoons and a pinch of Morton Kosher Salt
- 12 ounces penne pasta or other short pasta shape
- 2 tablespoons olive oil
- 2 large shallots, thinly sliced (about 2/3 cup sliced)
- 1 1/4 lbs cremini mushrooms or a mixture of mushrooms, trimmed and sliced
- 2 tablespoons dry sherry
- 2 teaspoons loosely packed chopped fresh thyme leaves, plus 2 or 3 sprigs
- 1/4 teaspoon freshly ground black pepper
- 8 ounces shredded gruyere
- 1 cup crème fraîche or sour cream
- 1 cup plain whole milk yogurt