Pomegranate and Fennel Chicken Pollastre amb Magrana

Name: Pomegranate and Fennel Chicken (Pollastre amb Magrana)
Ingredients: 1 (1.8 kg / 4 lb) chicken, butterflied (ask your butcher to do this for you); Sea salt flakes and freshly ground black pepper; Extra-virgin olive oil; 1 large onion, finely diced; 4 garlic cloves, minced, plus 1 garlic bulb, halved crossways; 1 fresh bay leaf; 2 large pomegranates, arils removed; 100 ml (3 1/2 fl oz) pomegranate molasses; 60 ml (2 fl oz / 1/4 cup) dry sherry; 2 tablespoons brown sugar; 1 red onion, sliced into 1.5 cm (1/2 in) thick rounds; 2 thyme sprigs; 1 fennel bulb, sliced into 1.5 cm (1/2 in) thick rounds, fronds reserved; 2 teaspoons fennel seeds; 25 g (1 oz) walnuts, roughly chopped; Salad leaves, to serve