1. For the Blue Cheese dressing: Add sour cream, buttermilk, mayonnaise and white wine vinegar into a medium-size bowl and stir until thoroughly mixed.
2. Season with dry mustard, garlic powder, Worcestershire and black pepper. Fold in Castello® Crumbled Blue cheese and set aside.
3. For the Salad: Cook pasta per instructions, drain and set aside.
4. Prep by chopping red onion and red grapes and set aside.
5. Add pasta, chicken and onions to a medium-size bowl and toss until thoroughly mixed.
6. Top with dressing and season with tarragon, salt and pepper. Gently fold in red grapes. Add walnuts if desired.