Rinse the chicken livers under cold running water. Drain well, pat dry and remove white connective tissue, if any; season liberally with salt and pepper.
Set a heavy bottomed skillet (cast iron preferred) with 1 or 2 tablespoons of cooking fat over high heat.
When the pan is really nice and hot, add the chicken livers and sear for about 45 seconds to one minute per side, just long enough for them to get a beautiful dark brown and crispy exterior but remain slightly pink on the interior.
Remove the liver to a plate and add the apples, onions, salt and pepper to the pan. Add more fat if necessary and cook over medium heat until both the onions and apple wedges start to caramelize and take a nice golden coloration, about 5 minutes total.
Deglaze the pan with the balsamic vinegar and then add raisins, hazelnuts and rosemary. Stir to combine, then add chicken livers and their juices back to the skillet. Give this one final stir, kill the heat, cover and allow to rest for about 5 minutes, to finish cooking the liver.
Meanwhile, add all the ingredients for the vinaigrette to a small food processor and process until smooth and creamy.
Divide the mixed greens and endive leaves between two plates and arrange the chicken livers and apples over the bed of greens.
Drizzle with the creamy hazelnut dressing and serve immediately.