1, Fill a large bowl with cold water to a depth of 3 inches and add the vinegar (this acidulated solution will retard discoloration in the cut banana blossom). Place the bowl near the cutting board. Remove and discard any worn or soft outer bracts from the banana blossom and any exposed flowers underneath. Using a sharp knife, cut off and discard the protruding stem at the bottom. Halve the blossom lengthwise. Make a V-shaped cut in the middle of each half to remove the solid off-white center core.
Place each half, cut side down, and cut it crosswise into half circles 1/ 16 to ⅛ inch thick. As you cut, pause occasionally to deposit the pieces into the vinegar water. (There should be enough water to cover the cut pieces. Add more water if necessary.) After cutting the entire blossom, let the pieces soak for 10 minutes.
2, Pour off the water from the bowl and replace it with warm water. Use your hands to massage the blossom gently for a minute. When the water turns cloudy, drain the blossom in a colander, and then rinse well under warm running water. Pick up handfuls of the blossom pieces, squeeze them to expel excess water, and put them in a large bowl. (Taste a piece of the blossom. If it is particularly astringent, discard about a quarter of the cut rounds of flowers, some of which will separate out to the bottom.) Add the bean sprouts and set aside.
3, Fill a small saucepan half full with water, add 1 teaspoon of the salt, and bring to a rolling boil over high heat. Drop in the pork (or chicken). When the water starts bubbling at the edges of the pan, remove the pan from the heat and cover tightly. Let stand for 20 minutes. The pork (or chicken) should be firm yet still yield a bit to the touch. Remove the pork (or chicken) from the pan and reserve the light stock for another use or discard. When cool enough to handle, cut the pork into matchsticks (or shred the chicken with your fingers into thin pieces, pulling the meat along its natural grain) and add to the banana blossom and bean sprouts.
4, In a mortar, crush the sesame seeds with the remaining 1 teaspoon salt and the sugar. Add to the salad along with the dried shrimp, peanuts, and Vietnamese balm, reserving a bit of the herb for garnish. Toss well to distribute the ingredients evenly. Add the lime juice, starting with 4 tablespoons. Toss well, taste, and adjust if needed with more lime juice, salt, and sugar. Transfer to individual plates or a platter, garnish with the reserved Vietnamese balm, and serve.