1 (10 ounce) package frozen chopped spinach, thawed
1 (6 ounce) can sliced mushrooms, drained
1 teaspoon dried minced onion
2 tablespoons balsamic vinegar
1 (10 ounce) package cream cheese
1/2 cup shredded Cheddar cheese
1 (6 ounce) can cream-style corn
½ cup shredded Swiss cheese
1 tablespoon shredded Monterey Jack cheese
Preheat oven to 350 degrees F (175 degrees C). Coat a 9x13 inch pan with cooking spray.
Place spinach in a large bowl and whirl in mushrooms. In a medium saucepan over a medium heat, combine vinegar and cream cheese; stir in mushrooms, onion and vinegar mixture. Bring mixture to a slow boil, stirring constantly, until sauce begins to boil. Stir in cheese, then pour mixture over spinach.
Bake in preheated oven for 50 to 53 minutes, or until a toothpick inserted into the center of the casserole comes out clean.