Cook pasta in a large pot of salted boiling water until al dente, about 8-10 minutes. Drain and rinse under cold water.

In a skillet, cook bacon over medium heat until crispy, about 6-8 minutes. Drain on paper towels, then crumble.

Make the dressing by mixing mayonnaise, sour cream, ranch seasoning, buttermilk, garlic powder, onion powder, salt, and pepper until smooth.

In a large bowl, combine cooled pasta, crumbled bacon, cherry tomatoes, diced onion, and cheddar. Toss gently.

Dress the salad with ranch dressing and mix to coat evenly.

Fold in chopped romaine lettuce just before serving to retain crunch.