One pot poached spring chicken

Name: One-pot poached spring chicken
Ingredients: 100g butter; 1 large chicken, about 2kg; 15 Jersey Royal potatoes, scrubbed and halved; 100g smoked bacon or pancetta lardons; 1 thyme sprig; 6 white peppercorns; 3 bay leaves; 250g carrots, tops cut off, halved lengthways; 200g bunch small turnips, peeled and halved; 150g podded peas; 150g podded and peeled broad beans; 8 spring onions, topped and tailed, then cut into 2cm lengths; 8 asparagus spears, trimmed; small handful parsley leaves, chopped; 1 small tarragon sprig, leaves picked; 1 lemon, cut in to wedges, to serve