Preheat the oven to 200°C/400°F/gas 6.
Put chicken breast in a bowl. Trim and wash a medium leek, remove the outer leaves, then slice it into 0.5cm/¼ inch pieces. Add these to the bowl with the leaves of a few sprigs of fresh thyme, a good lug of olive oil, a pinch of sea salt and freshly ground black pepper and a small swig of white wine and toss together.
Place your leek and flavourings from the bowl into the tray, then wrap the chicken breast in 4 slices of pancetta. This will not only flavour the chicken but also protect it while it cooks. Try and bend the sides of the tray in towards the chicken so the leeks don't burn during cooking. Drizzle with olive oil, place a couple of whole thyme sprigs on top and cook in the middle of the oven for 25 to 35 minutes.