Tiny, crunchy pickled gherkins.
Cornichon means gherkin in French. A gherkin is a small, young cucumber that's picked when it's still tiny, about 1-inch in length.
When pickled, these tiny bright green gherkins become sharply flavored. The flesh stays hard and crisp which makes them easy to slice -- either into tiny rounds or lengthwise to place on sandwiches. It also means they have a satisfying crunch when you bite into one. This matters because cornichons are often served with things that are soft. Like paté or smoked salmon.
I personally find cornichons too pungent to eat alone as a snack. But as a partner to other foods, I love their salty and vinegary personality. They have the same forwardness as capers and sometimes both of these pickled green little jewels are in the same recipe, as adding them to a good mayonnaise (in the classic French canon of sauces, this is called a sauce gribiche) to become a quick sauce for shellfish or meats.
Cornichons are usually sold in glass jars, alongside pickles. Some stores will sell them in barrels, similarly to olives. Because they're in a vinegar brine, cornichons will keep for a long time in your refrigerator.
I love to always have a jar on hand to place some alongside a slab of country paté, adding alongside a little dish of Dijon mustard, some sweet butter, a small mound of mesclun, and slices of the best French baguette I can find making a very easy first course for a dinner party.
I also like to add slices of cornichons to a pan cooked Berkshire pork chop because the little gherkins will stand up to the heat and add a spicy high note to a simply cooked meat. See our recipe.