Roast pork tenderloin with blackberry port sauce

Ingredients

• 2 pork tenderloins, just under 400 g (14 oz) each
• 1 slice of bread, crusts removed
• 1 small onion, quartered
• 2 cloves garlic, sliced, optional
• 4 cm (1½ inch) piece root ginger, peeled, sliced
• 40 g (1½ oz) walnut pieces
• Salt
• freshly ground black pepper
• 225 g (8 oz) blackberries
• 8 rashers smoked streaky bacon
• 5 small bay leaves
• 1 tablespoon olive oil
• 450 ml (¾ pint) chicken stock
• 150 ml (¼ pint) ruby port
• 2 teaspoons cornflour