A whole sole cooked in foaming butter until deep golden, finished with lemon and parsley. The flesh pulls cleanly from the bone and the beurre blanc on the side is silky, and rich. One of the great classic dishes of French cuisine!
Put the shallots, white wine, and vinegar in a small saucepan. Bring to a steady simmer and reduce until almost completely dry. You want the shallots soft and cooked down with just the faintest trace of liquid left in the pan. This takes about 10 minutes. Take the pan off the heat and let it cool for a minute.Now, over a very low heat, start adding the cold butter a few cubes at a time, whisking constantly. The butter should melt slowly into a creamy, glossy sauce rather than separating into oil. Keep adding the cubes and whisking until all the butter is incorporated. Season with salt and white pepper. Keep warm over the lowest possible heat or set the pan over a bowl of warm water. Don't let it boil or it will split.
2. Prepare the sole
Pat the sole thoroughly dry with kitchen paper on both sides. This matters for getting a good colour in the pan. Season generously with salt and pepper. Flour the fish at the very last moment before cooking. Put the seasoned flour on a large plate, press each sole into it on both sides, then shake off every trace of excess. You want the thinnest possible coating, not a crust.
3. Cook the sole
Heat the oil in a large frying pan over medium-high heat. Add the butter and let it foam. When the foam subsides and the butter turns a light golden colour, lay the sole in the pan carefully, presentation side down. Cook without moving for 3 to 4 minutes until deep golden underneath. Slide a wide spatula carefully under the fish and turn it. Cook for a further 3 to 4 minutes, basting the fish regularly with the butter in the pan. The sole is done when the flesh feels firm and lifts cleanly from the bone at the thickest point near the head. Transfer to warm plates.
4. Finish and serve
Squeeze the lemon juice over both fish and scatter the chopped parsley on top. Spoon the beurre blanc into a warm small bowl or jug alongside. Serve immediately with lemon wedges. Don't make anyone wait.
Notes
Ask your fishmonger to skin and trim the sole. Most will do it without a second thought and it saves you a fiddly 10 minutes at home.
Flour the fish at the last possible moment. If it sits for more than a few minutes the flour absorbs moisture and the coating goes claggy rather than crisp.
Cold butter is essential for the beurre blanc sauce. It is what creates the emulsion. If the sauce starts to look oily and separated rather than creamy, take it off the heat immediately and whisk in a couple of extra cubes of very cold butter.
If your pan isn't wide enough to hold both fish flat, cook them one at a time. A crowded pan drops the temperature and you lose the colour on the fish.
This dish does not wait well. Have everything ready before the fish goes in and serve straight away.