Take spinach out of the freezer the night before. When it has been thawed, place it between layers of paper towels and squeeze the water out of it until dry.
In a large mixing bowl mix together the spinach, sour cream, and soup mix.
Add the grated Parmesan cheese and stir until well combined.
Spray a 9" x 9" square baking dish or round 1-1/2 quart glass casserole dish with non-stick cooking spray and press the spinach mixture flat with a spoon or spatula.