How to Make It
In a large saucepan of boiling salted water, cook the potatoes until tender, about 15 minutes. Drain.
In a medium skillet, cook the bacon over moderate heat until crisp, about 4 minutes. Drain on paper towels and wipe out the pan. Melt 1 tablespoon of the butter in the skillet, add the leeks and cook over low heat, stirring, until softened, about 6 minutes. Season with salt and pepper.
Heat a 12-inch cast-iron skillet. Season the trout fillets with salt and pepper. Heat the oil in the skillet. Add the trout and cook over high heat until browned on the bottom, about 3 minutes. Turn the trout. Add the wine, potatoes, leeks and the remaining 3 tablespoons of butter. Simmer over low heat until the trout is barely done, about 4 minutes. Transfer the fish to warmed, shallow bowls. Simmer the vegetables until the wine taste mellows, about 4 minutes. Add the bacon and thyme and season with salt and pepper. Spoon the vegetables and sauce around the trout and serve at once.