01 - Place eggs in a saucepan and cover with cold water by 1 inch. Bring to a rolling boil over medium-high heat, then reduce to a gentle simmer and cook for 9 minutes. Transfer immediately to a bowl of ice water and let cool for 5 minutes. Peel and roughly chop the eggs.
02 - While the eggs cook, arrange bacon slices in a cold skillet. Set heat to medium and cook, turning occasionally, until evenly crisp and golden, about 6 to 8 minutes. Drain on paper towels, then crumble into small pieces once cool enough to handle.
03 - In a medium mixing bowl, combine the chopped eggs, mayonnaise, Dijon mustard, halved cherry tomatoes, crumbled bacon, and chives if using. Fold gently until evenly incorporated. Season with salt and pepper to taste.
04 - Spoon the egg salad mixture evenly into the center of each butter lettuce leaf, dividing it among all 8 leaves.
05 - Fold or roll each lettuce leaf around the filling and serve immediately while the lettuce is still crisp and cold.