The Cobb Salad was invented by Bob Cobb of the Brown Derby however another house salad the Derby Mixed Green Salad was very popular as a side dish.  In the Brown Derby Scene, episode “L.A. At Last!,” Lucy selects a tossed salad from the menu which the waiter explains is a mixed green salad. The Derby Mixed Green Salad recipe can be found in the  Brown Derby Cookbook.
Make your own Mixed Green Salad and  the Derby Old-fashioned French Dressing  to go with it from the original recipes pictured below from The Brown Derby Cookbook.

Derby Mixed Green Salad
Serves 4

1/2 head romaine cut in 1-in pieces
1/2 head (medium size) Lettuce, pulled
1/2 bunch watercress
1/2 head chicory
2 tomatoes,peeled and quartered
1/2 cup chopped celery
1/2 cup Brown Derby Old-fashioned French Dressing (see recipe below)

Toss the greens in a large cold salad bowl and mix lightly. Garnish with the tomatoes. Sprinkle chopped celery on top. Just before serving add French Dressing and toss lightly.

Brown Derby Old-Fashioned French Dressing, 1/ 1/2 qts.
This is the French Dressing which became so popular among the stars that the Brown Derby was prevailed upon to bottle it for home use. The cup of water is optional depending upon the degree of oiliness desired in this dressing.

1 cup water
1 cup red wine vinegar
1 tsp. sugar
Juice of 1.2 lemon
2 1/2 tbs.* salt
1 tbs. ground black pepper
1 tbs.  Worcestershire Sauce
1 tbs. English mustard
1 bead garlic chopped
1 cup olive oil
3 cups salad oil
(*Uk readers note a US tablespoon = British dessert spoon)
Blend together all ingredients except oils.  Then add olive and salad oils and mix well again. Chill. Shake before serving.

This dressing keeps well in the refrigerator. Can be made and stored in a 2 qt. Mason jar.