It's basically shredded/choppes spinach with white sauce added. Steam or quickly saute the spinach to cook it, then add white sauce to taste. The white sauce should be seasoned with a judicious amount of nutmeg or mace.
"white sauce" is traditionally a bechemel- Roux and milk accented with onion, clove and nutmeg. A chef I worked with a few years back cheated by adding creme fraiche to sauteed spinach- FANTASTICALLY DELICIOUS! (not to mention absurdly easy!)