Haricot vert beans, also known as filet beans, are a type of long slender green bean originally from France. This kind of bean can be difficult to find in conventional supermarkets outside of France, but is sometimes sold in specialty stores and farmer's markets. Similar to conventional green beans, these vegetables should be bright green, narrow in diameter, and crisp in texture, without any dark spots, rust, or mushiness. Preparing haricot vert beans works much like cooking other green beans, and you can use these French beans in salads, amandine dishes, and sautées, but take care not to overcook them.
Sometimes sold as French green beans or French string beans, haricot vert beans are slightly longer and thinner than conventional North American and UK varieties. Some seed catalogs refer to these beans as “filet” types. When cooked properly, these beans are crisp but tender, with a delicate but distinct flavor. You can substitute ordinary green beans in some recipes, but the result won't quite taste the same.
You can find French beans at supermarkets that offer a broad range of produce, at farm stands, or from some farmer's markets. This kind of bean may cost slightly more than an ordinary green bean. Sometimes, conventional green beans cut on a slant may be called French beans, but they are not the same as haricot vert beans.
The ideal bean is 6 to 8 inches (15 to 20 cm) in length, and about 0.25 inch (0.5 cm) in diameter, since larger haricot vert beans are often woody and tough. The bean should be bright green all over, with no sign of mold, rust, or mildew. Avoid beans with soft spots or dark areas, as they are usually past their prime and will produce an unpleasant taste and texture. If your beans are a little older than they should be, consider using them in a soup or stew, where their lower quality will be harder to notice.
Cooking haricot vert beans requires a little extra care compared to preparing thicker varieties, but is essentially the same. These beans cook well when steamed, stir-fried, or lightly boiled. They should never be cooked for long periods of time, since they easily become mushy and unpalatable. Combine these French green beans with onions, garlic, and butter, or consider tomatoes, almonds, or fresh salad greens. These flavors provide an interesting counterpoint for the taste of the beans, and keep the dish from becoming boring.