Cook bacon in a skillet over medium heat for 8 to 10 minutes until crisp, then drain on paper towels.
Boil farfalle in water with the tablespoon salt until fully tender. Drain, rinse briefly under cool water and drain thoroughly.
Whisk mayonnaise, buttermilk, vinegar, Dijon, dressing salt and pepper. Toss pasta with dressing, seeded tomatoes and half the bacon.
Fold in dry romaine and remaining bacon immediately before serving. For make-ahead, refrigerate the dressed pasta promptly and hold lettuce and reserved bacon separately.
Serve cool and refrigerate leftovers within 2 hours.