Given the task definition and input, reply with output. In this task, you have to identify the named entities (NER) which are the ingredients required given its directions. Named entities are the names of the items without their quantity.

Flatten out biscuits in baking dish., Saute chopped onions in margarine., Spread over biscuits., Cover with thickly sliced fresh tomatoes., Salt and pepper to taste., Spread 3/4 cup mayonnaise on tomatoes., Top with Cheddar cheese., Bake at 350 until it boils.
Butter, onions, margarine, tomatoes, salt, mayonnaise, Cheddar cheese