Cook pasta in a pot of salted water according to package directions. Drain pasta and place it in a large bowl. Drizzle over 1/2 cup of milk and toss.
In a small bowl or mason jar with a lid, add the mayonnaise, sour cream, 2 tablespoons milk, garlic, chives, parsley, salt, and pepper. Whisk together, or shake to combine.
Add chopped tomatoes, bacon, and lettuce to pasta. Drizzle over the dressing. Toss to combine. Taste and adjust seasoning. Serve immediately.