Slow cooker chilli con carne

Name: Slow cooker chilli con carne
Ingredients: 1 onion, sliced; 1 red pepper, deseeded and thickly sliced; small bunch fresh coriander, stalks finely chopped; 1 tbsp sunflower oil; 500g/1lb 2oz beef brisket, trimmed of excess fat and cut into matchbox-size pieces; salt and freshly ground black pepper; 2 fat garlic cloves, crushed; 1 tsp ground cumin; 1 tsp ground coriander; 2 tsp hot chilli powder; 1 tsp dried oregano; 2 tbsp tomato purée; 400g/14oz can chopped tomatoes; 300ml/½ pint hot beef stock; 2 x 400g/14oz can red kidney beans in water, rinsed and drained; 1 cube good quality dark chocolate, minimum 70% cocoa solids