Check out this lovely treatment of petrale sole from the New York Times - the key is to let the sauce thicken at the end!
1 ½ pounds Pacific sole or flounder fillets
Salt and freshly ground pepper
1 tablespoon extra-virgin olive oil
3 tablespoons finely chopped shallot
1 cup dry white wine (you can also use rosé; the sauce will have a pink hue)
FOR THE SAUCE
1 plump garlic clove, minced or puréed (more to taste)
2 tablespoons capers, rinsed and coarsely chopped
¼ cup fresh lemon juice
3 tablespoons extra-virgin olive oil
2 to 4 tablespoons finely chopped parsley
Preheat the oven to 400 degrees. Oil or butter one or two baking dishes large enough to accommodate the fish fillets in one layer. Lay the fish in the dish(es) and season with salt and pepper.
Heat the olive oil over medium heat in a small or medium skillet and add the shallot. Cook, stirring, until tender and translucent, about 3 minutes. Add the wine to the pan, bring to a boil, and pour the wine and shallots over the fish. Return the skillet to the stove (make sure the heat is off) for later use. Cover the baking dish with foil and place in the oven. Bake 8 to 10 minutes, or 5 minutes for each 1/2 inch of thickness, until the fish is opaque and pulls apart easily with a fork.
While the fish is in the oven, whisk together the garlic, capers, lemon juice and olive oil. You can also mash the garlic in a mortar and pestle and work in the capers, lemon juice and olive oil, though I prefer the capers chopped, even some intact, and not puréed.
When the fish is done remove it from the oven and carefully transfer to a platter or plates. Cover and keep warm. Pour the liquid in the baking dish into the skillet and turn the heat on high. Reduce, stirring often, to about 1/4 cup – it should be thick – and stir in the garlic and caper mixture and the parsley. Whisk together, taste and adjust seasoning, pour over the fish and serve.