In an electric deep fryer or a large and deep, heavy saucepan or stockpot no more than half filled with oil, heat the frying oil to 350°F. Place the flour in a large, shallow bowl near the stove and season it generously with salt and pepper.

In another large, shallow bowl combine the milk and buttermilk. Place a baking sheet lined with a double layer of paper towels in a low oven, and warm six dinner plates and a serving platter.
Dredge two of the trout fillets in the seasoned flour, then dip in the buttermilk mixture, coating both sides evenly. Dredge again in the seasoned flour and gently shake off the excess. Gently lower the two fillets into the oil. Cook for 4 to 5 minutes, until golden brown, nudging occasionally. Retrieve the fillets gently with a skimmer and transfer to the baking sheet.
Dredge and fry the next two batches of fillets in the same way. Transfer all the fillets to the hot platter and garnish with lemon wedges and parsley sprigs.
Serve with the Meunière Sauce passed in a sauceboat, on the side

Meunière Sauce

Prepare the Medium-Dark Roux, if you have not already done so. In a saucepan, melt the butter over high heat.   Add the celery, onion, green pepper, parsley, black pepper, bouquet garni and the clove. Sauté until nicely browned, about 4 minutes, stirring occasionally. Add the veal stock and lemon juice and bring to a boil. Boil for 2 minutes, then lower the heat and simmer the mixture gently for 10 minutes. Add a tablespoon of Roux and simmer for 2 to 3 minutes, until thickened. Keep adding Roux one tablespoon at a time until the sauce coats a spoon.
Season to taste with salt and a little more black pepper, and strain into a clean saucepan (or directly into the sauceboat, if serving right away), pressing down on the solids and scraping the bottom of the sieve to retrieve as much sauce as possible.