Mushrooms Florentine

4 tablespoons butter, melted, divided
1 pound medium-size whole mushrooms
1 teaspoon salt
1/4 cup finely chopped onion
2 (10 ounce) packages frozen chopped
spinach, thawed and drained
1 cup shredded Cheddar cheese, divided
Garlic salt, to taste

Heat oven to 350 degrees F.

Place 2 tablespoons of the butter in a large skillet over medium heat.
Add the mushrooms and cook until browned, browning the cap sides first.
Stir the salt, onion and remaining 2 tablespoons butter into the spinach.
Line a 10 x 7-inch casserole with the spinach mixture.
Sprinkle 1/2 cup of the cheese over the spinach.
Arrange the browned mushrooms over the cheese; season
with the garlic salt and top with the remaining 1/2 cup cheese.
Bake for 20 minutes or until the cheese is melted and browned.
Serve hot.