We just made this recipe up ourselves and, as a result, don't measure things out to the teaspoon. It is really important to have the right ingredients and then you can flavor it to your preference after that.
Mayonnaise (approx 2 cups)
Chopped dried green onion
Mix all but milk together initially with a wire whisk in a metal bowl. Once combined, add milk as needed to achieve desired consistency. Taste and add more ingredients until you get the flavor right. I know that sounds basic but it is really that easy! The biggest challenge is not using too much celery salt so go easy at first with that ingredient. The more black pepper the better - trust me!
Store in closed container in fridge for several days.
Now, not all missionaries have celery salt available to them so the next time you send a missionary a care package, throw in a bottle or two of celery salt from the dollar store! ;)