REMOVE all visible fat from pork and tie it into compact bundle with kitchen twine. Place pork into flameproof casserole or Dutch oven that is just large enough to hold it. Combine milk, water and lemon juice medium bowl; pour over pork. Cover; refrigerate for 24 hours, turning meat over every few hours. Remove from refrigerator about 30 minutes before cooking.
PREHEAT oven to 350° F. Remove pork from milk mixture; reserve milk mixture. Pat pork dry with paper towels. Season with salt and pepper. Heat oil and butter in large skillet over medium-high heat. Brown pork on all sides. Return pork and pan drippings to milk mixture in casserole.
STIR in garlic, onion, pancetta, bay leaves, thyme, mustard and beef broth; cover. BAKE for about 3 hours or until pork is tender. When done, the sauce will be reduced to curds.
TO SERVE, lift pork from dish onto warm serving platter; remove string and keep warm. Skim fat from sauce and remove bay leaves. With slotted spoon, spoon a portion of sauce around pork. Place remaining sauce into gravy or sauceboat.
NOTE: If a smoother sauce is desired, carefully pour half of slightly cooled sauce in blender container; cover with lid. Hold down lid with folded up towel. Blend until smooth. Repeat with remaining sauce.