In a small saucepan, over medium-low heat, warm the hot sauce. Stir in the butter and heat until melted.
Place the chicken pieces in a large bowl, pour the hot sauce mixture over the chicken, and toss.
In a small bowl, combine the sour cream, blue cheese, salt, pepper, and 2 1/2 tablespoons water. (If you prefer a thinner dressing, add more water, 1 teaspoon at a time.)
Divide the chicken and lettuce among individual plates. Drizzle the blue cheese dressing over the lettuce.