Wash the spinach in several changes of cold water.
Remove the coarse stems and heavy ribs.
Place in a large saucepan.
No water is needed as the drops on the leaves provide plenty.
Add the rosemary and green onion, tossing lightly to distribute among the leaves.
Cover and cook over medium heat 3-4 minutes or just until the spinach is wilted.
Shake the pot frequently during the cooking.
Toss with the salt, butter, and lemon juice.