Prepare the white sauce using a medium-low setting melt butter in a saucepan add flour and 1/4 teaspoon of salt until creamed together. Add milk a little at a time on medium heat. Constantly stir with a whisk until mixture becomes thick and smooth. Place butter in a 2-quart saucepan on medium heat, add onions.
Cook until the onions are transparent. Place spinach and add water to pan, lower the heat and place lid on pan. Stir several times until the spinach is almost completely cooked. Add 1 teaspoon of salt. When spinach is almost done add white sauce and sour cream, stir well and simmer until completely blended.
Want to make this creamed spinach extra creamy? Add two or three tablespoons of cream cheese to the sauce!
You can use a couple of paper towels to help you squeeze out some of the excess water in the frozen spinach.
To make this extra savory, consider adding a tablespoon or two of blue cheese into the sauce!