In a saucepan melt butter over medium heat until sizzling. If you are adding in the fresh garlic and a pinch of cayenne pepper then saute in butter for about 2 minutes but do not brown the garlic. Whisk in the flour and 1/2 tsp seasoned salt (or white salt) until creamed together and smooth. Stir in the half and half, or milk (if using) a little at a time. Increase heat to medium and constantly whisk until the mixture becomes thick and smooth. Remove from heat; set aside. Place 2 tbsp butter in saucepan over med heat; add the 2 tbsp minced onion, and cook until transparent. Add spinach and water to pan, lower the heat, and cover. Stirring several times until the spinach is cooked. When the spinach is almost done, add the prepared white sauce, sour cream and Parmesan cheese (if using). Stir well, and simmer until completely blended. Season with more seasoned salt or white salt if desired and black pepper.