Thaw the frozen spinach. Squeeze it dry with your hands. Make sure you get most of the water out or the dip will be runny.
In a large microwave-safe bowl combine the spinach, cream cheese, cheddar cheese, monterey jack cheese, sour cream, onion, brown mustard, and salt.
Microwave on HIGH for 2 minutes. Stir. Microwave another 2 minutes. Stir. Microwave 1 minute. Stir. Serve hot with tortilla chips, vegetable platter, crackers, or chunks of french bread.
Yield size: 4 cups.
