Preheat the oven to 400ºF / 200ºC degrees and line a baking sheet with foil.
Place crushed cornflakes into a bowl.
Brush the chicken breasts with 1/4 cup of buttermilk then season on both sides with the cayenne and salt and pepper.
Drop into the cornflakes and press to ensure that the cornflakes stick well to all sides.
Lay onto the baking sheet and bake for around 20 minutes until golden and crispy and cooked through (internal temperature should reach 165F).
In the meantime, mix together the sour cream, remaining 1/4 cup of buttermilk, vinegar and mustard and season with salt and pepper. Stir in the chopped tarragon.
Add in the lettuce and cucumber and toss to coat.
Lay the salad onto large plates. Slice the chicken and place on top of the salad then sprinkle with the chopped fresh chives.