Step 1Crush the peppercorns by placing them in a thick plastic bag and pounding it with a hammer, mallet or rolling pin.
Step 2Combine the crushed peppercorns, salt and sugar in a large resealable plastic bag.
Step 3Add the tuna and Armagnac to the bag, shaking to combine. Press out the remaining air, seal and let sit in the refrigerator for 24 hours, shaking the bag once or twice.
Step 1In a mortar, crush the garlic and anchovies into a thick paste with a pestle.
Step 2In a food processor, place the crushed garlic and anchovies, the capers, olives, olive oil, lemon juice and parsley and process until very smooth. Reserve. Makes 1 cup.
Step 1Put the potatoes in a pot large enough to hold them comfortably. Add salt and cold water to cover. Cover the pot and bring the potatoes to a boil.
Step 2Simmer the potatoes until almost cooked, 25 to 30 minutes, depending on their size, being careful not to overcook them. The potatoes should be tender enough to allow a fork to be inserted, but not mushy. Drain and rinse under cold water. Refrigerate until the potatoes are cold, preferably overnight.
Step 3Remove the peel and cut the potatoes lengthwise into thin slices, about one-eighth-inch thick, allowing for at least nine slices. Discard any scraps or broken slices. Cut each slice of potato in half crosswise so that you have 18 pieces.
Step 4Scrape the seasoning from the gravlax and slice it very thinly, being sure to cut through the grain.
Step 5Place a piece of potato on the center of each of six plates, spread a thin smear of creme fraiche over each piece, then layer a piece of gravlax; repeat two more times, ending with gravlax.
Step 6Garnish each plate with two whole caper berries and a mound of tapenade. Any leftover tapenade can be refrigerated and used for another purpose.