In a food processor, combine the mustards, soy sauce, pepper, thyme and garlic. Process until smooth. Rub all over the pork roast, loosely cover with plastic wrap and refrigerate at least 6 hours. Remove from refrigerator and allow to rest at room temperature for 30 minutes before cooking.
Preheat the oven to 350 degrees F. In a roasting pan, add the fennel, onions and carrots. Drizzle with olive oil and season generously with salt and freshly cracked pepper, to taste. Put the bread crumbs on a plate wide enough to fit the loin. Carefully roll the pork in the crumbs to form a nice crust. Put the pork on top of the vegetables in the roasting pan and bake until the internal temperature reaches 165 degrees F on an instant-read thermometer, about 2 to 2 1/2 hours.
Remove the pork from the oven to a cutting board and let rest. Put the roasting pan over 2 burners on high heat. Add the vermouth and chicken stock and let reduce by half. Season, to taste, with salt and pepper. Whisk in the butter and strain into a small pitcher or bowl.
Remove the pork from the bone and slice into serving portions. Arrange on a serving platter and drizzle with the jus.