In a large bowl or tall container, combine the egg yolk, lemon juice, and mustard. Using an immersion blender (or a whisk), start blending while gradually adding the olive oil in a thin stream until the mixture becomes thick and creamy. Season with salt to taste.
In another bowl, gently mix the crab meat with the chopped dill, chives, and lemon zest. Add the desired amount of homemade mayonnaise — you may not need all of it, depending on the consistency you prefer.
Heat a frying pan over medium heat. Lightly butter the rolls and toast them for a few minutes on each side until golden and crispy.
Place a few Boston lettuce leaves inside each toasted roll, then generously fill with the crab mixture.
