1Heat a medium sauté pan over medium heat for 1 minute. Add the butter, and when it foams, stir in the red onion. Add the thyme, a healthy pinch of salt, and a pinch of black pepper. Sauté about 10 minutes, until the onion is translucent and soft. Add the sorrel to the pan, and stir to combine. Turn the heat up to medium-high, add the cream, and cook, stirring continuously, about 3 minutes, as the cream reduces and coats the onions. Taste for seasoning, and transfer to a plate to cool completely.
2Lay the trout, skin side down, on a cutting board, open like a book. Season lightly with salt and pepper, and spread the sorrel onions on one side of each fish. Fold the fish back together, and wrap each trout with a piece of pancetta, spiraling the meat around the fish like the stripe on a candy cane. Refrigerate the fish until 15 minutes before cooking.
