Marinate the chicken in the buttermilk (with a li'l bit of salt) for about an hour or more.
Preheat oven to 210 c (which is about 425 F).
Put the walnuts, parmesan and black pepper in your food processor and whizz it around for a bit. Tip out onto a plate.
Take the chicken out of the fridge and carefully dip each piece into the walnut mixture after letting most of the buttermilk drip off.
Stick them on greaseproof paper and bake in the oven for about 40 minutes.