Preheat the oven to 180°C, fan 160°C, gas 4.
Heat half the vegetable oil in an ovenproof casserole or deep sauté pan (at least 2.75-litre capacity). Ours had a 25cm diameter and was 8cm deep. Brown the sausages for 3-4 minutes,turning regularly; they don’t need to be cooked through at this point. Remove to a board and cut each one into 3 chunky pieces. Set aside.
Fry the onion and bacon in the rest of the oil, in the same pan, for about 5 minutes, stirring occasionally. Stir in the thyme, plus the flour if you’d like a slightly thickened sauce, then take off the heat. Stir in the carrots, bay, sausage chunks and half the potatoes. Season well, then shake the pan to give a fairly even layer.
Arrange the rest of the sliced potatoes on top, to cover. Pour in the stock, then return to the heat and bring up to a simmer. Dot the butter over the top of the potatoes, season, then cover with a lid or use baking paper and foil.
Bake the coddle in the oven for 1 hour, then remove the covering and cook for a further 30 minutes. The veg will be tender and the top lovely and browned when it’s ready to serve.
