Italian-style chicken drumsticks

Ingredients (serve 4): 1 tablespoon olive oil 2 sticks celery, thinly sliced 100g pancetta or bacon, chopped (optional) 2½ cups cooked tomato sauce (see related recipe) ½ cup chicken stock 12 chicken drumsticks 1 lemon, cut into wedges ¾ cup black or green olives 1/3 cup flat-leaf parsley leaves, roughly chopped   Method: Preheat oven…