Place peppercorns in plastic food storage bag to contain and crack them with mallet or small pan to a very coarse grind. Combine peppercorns with pork, garlic, thyme and some salt. Make 4 thick patties, thinner at the center for even cooking.
Heat the extra-virgin olive oil over medium-high heat. Cook 6 minutes on each side. Set burgers on bread slices or bun bottoms. Top with lettuce, sliced gherkins and sliced shallots. Combine the cranberry sauce with the mustard and slather on bun tops. Place the tops on the burgers and serve.