Step 1

Cook spaghetti according to package directions; drain. Spoon into a lightly greased 13- x 9- x 2-inch baking dish; set aside.

Step 2

Combine spinach and next 6 ingredients; spoon over spaghetti.

Step 3

Remove casing from sausage. Cook sausage and onion in a large skillet over medium-high heat until meat is browned, stirring to crumble. Drain well. Sprinkle sausage mixture over spinach mixture.

Step 4

Combine egg and ricotta cheese; spread over sausage mixture. Cover and chill 8 hours.

Step 5

To bake, remove casserole from refrigerator, and let stand at room temperature 30 minutes. Bake, covered, at 375° for 35 to 40 minutes or until thoroughly heated. Sprinkle top with tomato and parsley.