What can I do with leftover buttermilk?

Q. What's to be done with leftover buttermilk?

A. Such was my dilemma after I bought a quart of buttermilk and then made a recipe that required less than a cup.

So what, exactly, is buttermilk? Traditionally, it was a byproduct of butter making: If you churn cream long enough, you wind up with butter and ... buttermilk. Despite its reputation as a high-fat product, buttermilk was the butterless part of the deal.

In the olden days, milk destined for butter production was allowed to sit for a while to allow the milk and cream to separate. During this period, naturally occurring lactic-acid-producing bacteria would begin to ferment the milk; this made the butter easier to churn and had the effect of giving the buttermilk a distinct, acidic tang as well as a thickened, "clabbered" texture.

Nowadays, the buttermilk you see in the supermarket is what's known as cultured buttermilk. It is made by adding a culture of lactic-acid-producing bacteria to regular milk in order to achieve the tang. The fat content of cultured buttermilk depends on the milk used to make it and, thus, can vary between 0 percent (nonfat milk) and 3 1/2 percent (whole milk). A low-fat buttermilk, whose fat content ranges between 1 1/2 and 2 percent, is what I prefer.

(When buttermilk is used in baking, the acid in it must be neutralized with an alkali. That's why buttermilk biscuits and Irish soda bread are made with baking soda, an alkaline leavening, and not baking powder, a neutral.)

But I was fretting over leftover buttermilk. I could have made biscuits or soda bread or pancakes, but that seemed like too much trouble. Instead I made a buttermilk salad dressing that I've been enjoying ever since.

BUTTERMILK DRESSING 

1 cup buttermilk

1/2 cup mayonnaise

1/4 cup extra-virgin olive oil

2 tablespoons Dijon mustard

Pinch garlic powder

2 tablespoons lemon juice

Salt

Pepper

Whisk all ingredients together, or place in a large, tightly sealed jar and shake vigorously. Makes about 2 cups dressing. Store in the refrigerator for up to a week.

Q. Why don't restaurants tell you the price of the daily specials?

A. Some restaurants do, either by printing them out or by instructing the servers to include them in their recitations. These restaurants should be commended.

As for restaurants that keep those prices a secret, I can only speculate that they are trying to score a few extra bucks. I've had restaurateurs tell me that they don't share the prices because doing so can embarrass customers, or make them feel cheap. Frankly, if a waiter wants to embarrass me, he should point out that I've eaten more than my share of the free olives. Telling me that the branzino costs $32 isn't going to do it.

Of course the diner has a very effective recourse here: Ask the waiter the prices ... if you're not too embarrassed.