1. Slice the pork fillet into thin strips, about 1/4 inch or 6 millimeters, and brown them in 2 tablespoons or 30 grams of butter in a skillet over medium heat, which is approximately 180°C or 350°F. Season with salt and pepper to taste. Transfer the browned meat to a large Dutch oven or heavy pot.

2. Slice the onion and leek into thin rings and sauté them in 1 tablespoon or 15 grams of butter until softened, which should take about 5 minutes. Add the sautéed vegetables to the pot with the pork, along with 2 cups or 475 milliliters of water, 1/2 cup or 120 milliliters of crème fraiche, 1 teaspoon or 5 grams of mustard, 1 teaspoon or 5 grams of green peppercorns, and 1 tablespoon or 15 milliliters of soy sauce. Bring the mixture to a boil, then reduce the heat to low, approximately 150°C or 300°F, and simmer for 15 minutes.

3. Cut the bacon into small pieces, about 1/2 inch or 1 centimeter, and cook in a skillet over medium heat, approximately 180°C or 350°F, until crispy. Drain the bacon on paper towels. Peel, core, and slice the apples into thin wedges, about 1/4 inch or 6 millimeters, then sauté them in the same skillet with the crispy bacon until lightly caramelized, which should take about 5 minutes. Add the apple-bacon mixture to the pot and simmer for an additional 10 minutes.

4. Taste the stew and adjust the seasoning as needed. Serve the stew hot, garnished with chopped parsley and accompanied by boiled potatoes and cornichons.