Cook the Pasta: Begin by bringing a large pot of salted water to a rolling boil. Add the rotini pasta and cook according to package instructions until al dente, about 8-10 minutes. Drain and rinse under cold water.

Combine the Salad Ingredients: In a large mixing bowl, combine the cooled pasta, cubed cheddar cheese, sliced dill pickles, and chopped onion. Toss gently until well-mixed.

Whisk Together the Dressing: In a separate bowl, whisk the mayonnaise, sour cream, pickle juice, dill, salt, and pepper until smooth.

Mix the Dressing with the Salad: Pour the dressing over the pasta mixture and toss until evenly coated.

Chill the Salad: Cover with plastic wrap or transfer to an airtight container. Refrigerate for at least two hours.

Final Touches Before Serving: Stir the salad before serving and add a splash of mayonnaise or pickle juice if dry. Adjust seasoning as needed.