Dry-fry the pancetta over a high heat, until crispy and cooked through (about 5 minutes), then remove with a slotted spoon and drain on kitchen paper. Add the butter to the pan and allow to melt, then add the sprouts, a little ground black pepper and a splash of water. Cook over a medium heat for 10-15 minutes, until tender. Stir through the chestnuts and pancetta, heat through and serve immediately.
