Veal kidneys (rognons de veau) are the most prized of the French offal cuts — their firm, almost meaty texture and clean, mineral-sweet flavour make them suitable for the finest restaurants. Flambéed with Cognac and finished with mustard cream, they represent the rôtisseur's mastery of rapid, high-heat offal cookery. The kidney must be veal (rognon de veau), which has a pale rose colour and mild flavour — lamb kidneys are acceptable but stronger; beef and pork kidneys are too pungent for this preparation. Preparation: peel the transparent outer membrane, halve the kidney lengthwise, and remove the core of white fat and sinew (this fat has an unpleasant, urinous flavour if left in). Cut into 2cm thick slices or leave in halves for a more dramatic presentation. Season. Heat a heavy sauteuse until very hot, add clarified butter, and sear the kidney pieces for 2 minutes per side — the exterior should be mahogany brown while the interior remains distinctly pink (55-60°C; kidney cooked past 65°C becomes grey, rubbery, and releases an unpleasant liquid). Remove and rest on a warm plate. Deglaze the pan with 50ml Cognac, flambée until the flames die, add 2 minced shallots, cook 30 seconds. Add 100ml veal jus, reduce by half. Finish with 2 tablespoons double cream and 1 tablespoon Dijon mustard — the mustard goes in off the heat (boiling it produces bitterness). Return the kidneys to the sauce briefly to coat. Serve immediately in a cocotte or on a warm plate with the sauce pooled beneath.
Remove ALL the white core fat — it has a urinous flavour that taints the dish Sear quickly at very high heat — 2 minutes per side for pink interior (55-60°C) Never exceed 65°C internal — overcooked kidney is grey, rubbery, and releases bitter liquid Flambée the Cognac to burn off harsh alcohol — the residual caramelised sugars add depth Mustard added off the heat — boiling destroys its pungency and creates bitterness
Leave the kidney whole, roast it surrounded by its own fat (en robe) at 200°C for 15 minutes, then rest and carve — the fat bastes it during roasting and the centre is perfectly pink A splash of port wine instead of Cognac produces a sweeter, more rounded sauce Scatter a few capers and cornichons into the sauce at the end for a version recalling sauce diable — the piquancy pairs brilliantly with the kidney's mineral character
Leaving the white fat core in — its strong, unpleasant flavour contaminates the entire dish Overcooking — kidney that has released grey liquid is irredeemable; it is done when still firmly pink Using a pan that is not hot enough — the kidney stews, releasing liquid instead of developing a crust Boiling the mustard — it turns bitter and acrid; stir it in off the heat at the very end Serving on a cold plate — the kidney cools rapidly and the fat in the sauce congeals
Escoffier, Le Guide Culinaire; Larousse Gastronomique