Heat a tiny drop of olive oil in a nonstick frying pan, or the bowl of your slow cooker if it can go on the hob. Once the oil is hot, add in the pancetta and cook until deeply golden and crispy. Use a slotted spoon to remove the pancetta from the pan and drain on some kitchen towel. Drain away all but about 1 tablespoon of the fat and fry the beef until crispy and golden.
Sautee the onion, celery and garlic in the frying pan or in the bowl of your slow cooker. Once the vegetables are tender stir the beef, pancetta, and vegetables together in the slow cooker.
Add in the tinned tomatoes and beans. If you're using the new Aldi mixed beans with spicy tomato sauce then add in the whole tin. If using regular kidney or mixed beans, be sure to drain and rinse them first.
Season with chilli powder, cumin and dried thyme. Go easy with the salt at this stage. You can taste and adjust after the cooking time.
Cook on low for about 4-5 hours or longer. Alternatively, it's no problem to cook this chilli on high for about 3 hours. Once the chilli is cooked, stir in a tablespoon of cocoa powder. Be sure it's unsweetened!