Add spinach and water to a skillet, place over medium heat and cook approximately 3−4 minutes, tossing occasionally—just until the spinach is wilted and bright green. Remove from heat, transfer spinach to a colander or strainer then press it against the sides of the strainer, using the back of a spoon to remove as much liquid as possible.
Next, move the spinach to a cutting board, chop coarsely then set aside.
Return the skillet to medium-low heat and melt the butter. Add onion or shallot and garlic, and cook approximately 3−4 minutes until tender and translucent. Add flour, stir until dissolved in the butter, cook 1 minute then add milk. Stir until the flour is completely dissolved. Add salt and pepper then heat until the mixture begins to bubble and thicken. Add Parmesan cheese and stir until the cheese is melted and completely incorporated. Reduce heat to low and simmer approximately 2 minutes, stirring constantly.
The last thing to do is to add the chopped spinach to the cream sauce. Stir to incorporate then cook until the spinach is heated through and the dish reaches the desired consistency.
Transfer to a serving dish and enjoy!
One Last Thing
If your finished product is too thick, just add a little milk until you get the desired consistency. Delish!