Preheat oven to 400 degrees F. Allow the pork to come to room temperature for 30 minutes. Place the pork, fat side up in a roasting pan just large enough to hold it comfortably.
In a small bowl, whisk together the olive oil, 2 teaspoons of each mustard, the ground fennel, 2 teaspoons salt and 1/2 teaspoons black pepper. Rub the mixture on top of the pork and roast for 1 to 1 1/4 hours, until the internal temperature reaches 140 degrees F.
Remove from the oven and transfer to a cutting board and cover tightly with foil for 20 minutes, while you make the sauce.
For the sauce, remove all but 1/4 fat from the roasting pan. If there isn't 1/4 cup, add enough butter to the pan to make 1/4 cup total. Over medium heat, whisk the flour into the fat and cook for 1 minute. Add the wine and scrape up all the brown bits from the bottom of the pan. Add the chicken stock, remaining 2 teaspoons of each mustard, the green peppercorns, 2 teaspoons salt and 1/2 teaspoons black pepper. Bring to a boil, then lower the heat to a simmer for 5 to 10 minutes, until the sauce is reduced and slightly thickened.
Serves 8 generous portions. I served it with mashed or roasted potatoes and homemade applesauce. I'll share the delicious purple cabbage recipe in an upcoming post.