You can vary this dressing and make it creamy by adding half a cup of mayonise, sour cream or Greek yogurt. 

Mustard is an emulsifier – it helps keep the oil from separating from the rest of the ingredients.  When I made this with the blender, it became very thick so I stirred in some additional oil by hand.

 Ingredients:

• 1/2 c sugar
• 2 tsp finely chopped onion
• 1/2 tsp salt
• 1/3 c lemon juice
• 1 tsp Dijon mustard
• 2/3 c  oil
• 1 Tab poppy seed

Directions: 

1. Using a hand mixer (or blender or food processor) on low speed, combine sugar, onion, salt, lemon juice and mustard.
2. Add oil in slow steady stream until well blended.
3. Add poppy seed.

Servings: 12

Source:  Karen Eckardt from the Midway Road Baptist Church (Dallas, TX) cookbook. Also, an old favorite, Betty Crocker.