1 lg. sweet Spanish onion
3 c. thinly sliced zucchini
2 tsp. butter
2 eggs, beaten
1/2 c. sour cream or yogurt
1 tsp. salt
1/8 tsp. pepper
1/2 tsp. dry mustard
1 c. grated Swiss cheese

Peel and thinly slice onion, separate into rings (should measure about 3 cups). Saute onion and zucchini in butter until tender. Place in shallow 1 1/2 quart baking dish. Combine eggs, sour cream or yogurt, salt, pepper, mustard and half of the cheese. Pour over vegetables. Sprinkle with remaining cheese. Bake at 375 degrees for 20 minutes or until firm. Serves 6.