Remove outer leaves of lettuce and wash thoroughly in cold water. Drain and pat dry with paper towels then split into wedges and arrange on plates. Scatter grape tomato halves over and around the lettuce.
Make dressing by combining mayonnaise and sour cream in a large mixing bowl. Squeeze in fresh lemon juice, fold in blue cheese and chives and season with salt and pepper. Pour dressing over wedge and grape tomatoes. Drizzle with a little extra-virgin olive oil and top with chives.