Preheat the oven to 400 degrees Fahrenheit (200 degrees Celsius).
Season: Pat dry the chicken portions, sprinkle them generously with salt and pepper on both sides. Place in a shallow oven dish, close to each other, there should not be any space in between the chicken breasts, otherwise, some of the glaze will seep to the bottom of the pan.
Roast the hazelnuts in a pan without adding any fat until fragrant. Remove to a large plate, let stand until cool enough to handle, then rub them between your palms to remove as much of the brown skins as possible; you don't have to remove every bit of it. Chop the hazelnuts roughly.
Make topping: Chop the onions finely. Heat the oil in a pan and cook the onions until golden. Add the hazelnuts, stir well for a couple of minutes, then add the Cognac and the apricot jam. Mix well and pour this mixture over the chicken.
Bake: Cover the dish with aluminum foil, ensure that the foil doesn't touch the chicken, and bake for 20 minutes. Remove the foil and continue baking, uncovered, for about 10-15 minutes or until the chicken is cooked through and the glaze is sticky.
Serve: Sprinkle with chives and serve immediately with green salad and baguette or rice.