Spinach-Steamed Mussels with Thin Spaghetti

Melt butter in a large stockpot over medium heat. Add onion, garlic, and bay leaf; sauté 3 minutes. Add tomato, salt, and spinach; cover and cook 4 minutes; stirring once. Add wine and mussels; bring to a boil. Cover and cook 5 minutes or until mussels open; discard any unopened ones. Discard bay leaf. Remove mussels with a slotted spoon. Arrange 1 cup pasta on each plate; top with about 9 mussels. Ladle 1/2 cup spinach sauce over each serving; sprinkle with pepper.