If you’re using fresh spinach, sauté a handful at a time in a frying pan without oil. As the spinach becomes soft, transfer to a bowl and sauté another handful. Continue until all the spinach is cooked. If you are using frozen spinach, thaw until soft.
Whether you are using the cooked fresh spinach or thawed frozen spinach, squeeze the excess liquid from the spinach. You should have dry spinach before you add anything!
Finely chop the spinach and place in a medium bowl.
Add the sour cream, cream cheese, Parmesan, mozzarella, garlic, granulated onion, and salt to the bowl.
Mix the ingredients until combined.
If desired, chill the spinach dip so it thickens up, and then serve with a dusting of shredded Parmesan and fresh herbs or chopped green onions as a garnish.