Frog Soup
(Normandy.) To 1 1/2 quarts of white stock, add 1 1/2 ounces of flour, an onion, parsley, celery, salt, and pepper. Cook it 1 hour, strain and add 1 dozen frogs' legs, fried in butter, and a glass of sherry. Cook 1/2 hour more, add the yolks of 2 eggs, blended with 1 cup of hot milk and a little butter.
A classic velouté-style soup finished with an egg-and-milk liaison. Two points decide whether it works: the liaison must never boil, and the frogs' legs do not want half an hour of simmering.
- The liaison is the hingeOnce the yolks blended with hot milk go in, keep the pot below a simmer — around 170F. Boiling curdles the yolks and the soup turns grainy. Temper by whisking a ladle of hot soup into the yolk-milk mixture before it goes back into the pan, and serve immediately.
- Frogs' legs, timingThe recipe's "1 dozen frogs' legs" may mean twelve single legs (six pairs) rather than a dozen pairs. Either way, legs fried in butter are essentially cooked already, and the further half hour called for will leave them stringy. Simmer the fried legs in the strained stock for five minutes or so to flavour it, then pull the meat from the bones and return it at the end.
- White stockAn unroasted veal or chicken stock, pale and unsalted. 1 1/2 quarts is 6 cups. Use a light chicken stock if veal bones are not to hand, and keep it unseasoned since the recipe salts separately.
- The flour1 1/2 ounces is about 1/3 cup. The recipe does not say how it goes in; adding it dry to hot liquid will give lumps, so work it into a little cold stock or cook it in butter first. A roux of equal butter and flour, cooked without colouring, is the reliable route.
- "A glass of sherry"In cookbooks of this era a wine glass runs roughly 2 to 4 fluid ounces. Start with 1/4 cup of dry sherry (fino or amontillado, not cream) and add more to taste after the soup has simmered.
- Vegetables and strainingOne onion, a few parsley stalks and a rib or two of celery, all left in large pieces since everything is strained out after the hour. Strain through a fine sieve; the soup should be smooth and pale before the legs go in.
- Sourcing frogs' legsSold frozen, often in pairs, at Asian and specialty markets; twelve pairs would come to roughly 1 1/2 to 2 lb bone-in, though sizes vary a good deal. Thaw and pat dry before frying or they will not brown.
- YieldSix cups of stock plus the finishing milk gives six to eight first-course servings. It does not reheat well once the yolks are in — make it to serve.
Frogs have been eaten in France since at least the Middle Ages, and by the end of the eighteenth century the English were using "frog" as an epithet for the French. The Normandy attribution here is plausible in spirit — the region's cooking leans on butter, cream and egg-yolk enrichments, all three of which finish this soup — though a frog soup thickened with flour and mounted with yolks is really the standard nineteenth-century French potage template with frogs' legs substituted for chicken or veal. Books of the period called this finish a "liaison." The frog legs themselves were less exotic then than now: American markets sold wild-caught legs seasonally, and cookbooks treated them as a delicate white meat closer to chicken than to fish.