Blue Cheese Buttermilk Dressing

2 cups mayonnaise
1 tsp lemon juice
1 tsp white vinegar
1/4 cup buttermilk
1/2 cup sour cream
1/2 tsp salt
1/4 tsp pepper
1/4 tsp garlic powder
4 oz blue cheese, crumbled

Combine mayonnaise, lemon juice, vinegar, buttermilk, sour cream, salt, pepper, and garlic powder. Gently stir in blue cheese. Cover tightly and chill for several hours, or overnight.