Put a pot of water to boil with salt. Wash spinach. Put spinach in boiling water and cook for 3 minutes at a slow boil.
Drain spinach and run cold water over spinach to stop it from cooking. A handful at a time, squeeze the spinach to get the water out. Chop. (You can now store, refrigerate and continue whenever.)
In a pot on medium heat, melt 2-3 tablespoons of butter, then put spinach in and stir. Cover for a minute or two.
Add 2-3 tablespoons of flour and stir until the white dissolves. Really make sure white dissolves!
Add a little salt and pepper and grate nutmeg for 9 seconds. Stir. Add 1/2 Knorr stock cube (chicken or beef preferably) and continue to stir while gradually adding 1 cup of water. Be sure the stock dissolves completely!
Correct seasoning. At the end you could add another 2-3 tablespoons of butter.
Take off heat. It’s really important not to cook it too long, either while you’re preparing it or when you heat it up to serve later! You just want it gently heated. Overcooking is what kills it.