So, did you see thatNew York Times article about LiquiGlide? The one with the videos that show mayonnaise sliding out of its bottle so gracefully, without leaving a trace behind? LiquiGlide makes the inside of tubes slippery enough that no drop of ketchup (or toothpaste, or mustard) is wasted, but bottles with this technology won't be on the market until at least later this year. What are we going to do until then?
We're going to make dressings in the bottle. This is the same principle as shaking a salad dressing in a jar. Only here, you shake directly in a (mostly) used up ketchup, mayonnaise or mustard bottle, using the stubborn mayonnaise/ketchup/mustard that's sticking to the sides of said bottle as the dressing's base.
(And, actually, it's not just salad dressing you can make this way. There are dipping sauces, too.)
The technique is almost too simple to explain, but here goes: 1. Twist the cap off the bottle. 2. Pour oil, vinegar, or other saucy ingredients into the bottle. 3. Replace cap (firmly). 4. Shake.
How much oil/vinegar/juice you add will depend on how much mayo/ketchup/mustard is in the bottle; a good rule of thumb is to make your mixture about 1/3 acid. Go ahead and eyeball this, and add non-acidic ingredients to taste. You can always fix a dressing later by adding a little more oil, or even some water to thin it out. Here, a few of the endless options.
ketchup
Curry Powder + Lime Juice
Sherry Vinegar + Chopped Shallot
Soy Sauce + Sriracha
mayonnaise
Lemon Juice + Olive Oil + Chopped Herbs
Tabasco Sauce + Lime Juice + Olive Oil
Orange Juice + Chopped Mint
mustard
Olive Oil + White Wine Vinegar + Chopped Herbs
Rice Vinegar + Honey
Apple Cider + Cider Vinegar + Olive Oil