Step 1

Cook pasta according to package directions. Drain; set aside.

Step 2

Preheat oven to 350°F and lightly grease (or spray with nonstick cooking spray) a 1 ½ quart casserole or baking dish.

Step 3

While pasta is cooking, heat oil in a skillet over medium high heat. Add mushrooms and onions, sprinkle with salt and pepper. Sauté for 6-7 minutes or until mushrooms are golden and onion is soft. Add garlic and cook, stirring, for 1 minute more. Remove from heat.

Step 4

Combine egg, 1 cup Monterey Jack cheese, sour cream, milk, 2 tablespoons Parmesan, pepper, and nutmeg in large bowl. Add spinach, mushroom mixture, and cooked spaghetti; mix well.

Step 5

Place in prepared casserole dish. Sprinkle with remaining Monterey Jack and Parmesan cheese.

Step 6

Bake, covered, for 25 minutes; remove cover and bake for another 20 minutes or until bubbling and golden brown. If desired, check internal temperature with instant read thermometer inserted in center of casserole; it should read 165°F.