1. Preheat oven to 375°. Put hazelnuts on a baking sheet and bake 10 minutes. Wrap nuts in a clean kitchen towel and rub vigorously to remove as much skin as possible. Roughly chop nuts and set aside.
2. Fill a medium saucepan with water and bring to a boil. Add 1/2 tsp. salt, chives, tarragon, and parsley. Cook 30 seconds; drain. Rinse herbs with very cold water and use your hands to squeeze out as much water from them as possible. Chop herbs and put in a blender.
3. Add oils and whirl until herbs are puréed, 2 to 3 minutes.
4. In a small bowl, whisk egg yolk and mustard together. Add a drop of the herb-oil mixture and whisk until fully incorporated. Repeat with the remaining herb-oil mixture, adding only 1/2 tsp. at a time to create a thick, mayonnaise-like dressing. Whisk in remaining 1/4 tsp. salt, the lemon juice, and pepper. Add more salt and pepper to taste if you like.
5. Tear lettuce leaves into bite-size pieces and put in a large bowl. Toss gently but thoroughly with dressing. Garnish with reserved hazelnuts and serve immediately.
Note: Nutritional analysis is per serving.