Cook the pasta in well-salted water according to the package directions until al dente. Drain and rinse briefly under cold water, then drain thoroughly so the dressing will cling properly.

Cook the bacon until crisp, drain it on paper towels, cool, and crumble. Reserve a little bacon for sprinkling over the salad just before serving.

Whisk the mayonnaise, sour cream, ranch seasoning, milk or buttermilk, garlic powder, and black pepper in a bowl until smooth. The dressing should be slightly looser than the final consistency because the pasta will absorb some moisture.

Place the cooled pasta, most of the bacon, tomatoes, onion, and optional cheddar in a large bowl. Pour over the dressing and toss gently until every piece is coated.

Fold in the chopped lettuce shortly before serving so it stays crisp. Refrigerate the salad for 20 to 30 minutes if time allows, then stir and loosen with a small splash of milk if needed.