1 Set the oven to 180 degrees.
2 Put the butter, onions, garlic, bacon and thyme into a pot along with a splash of water. Cover and cook on a medium heat for 15 minutes.
3 Remove the lid and continue to cook for five more minutes until the juices evaporate and the onions start to colour.
4 Take off the heat and add the chicken, mustard, red wine vinegar, salt and pepper, then fold everything together.
5 Take your largest casserole dish or a medium sized, deep roasting tray and add a ladle of stock to the base, followed by one-third of the potatoes. Arrange evenly then season the top.
6 Add half the chicken and onion mix then spread it out over the potatoes.
7 Lay the next third of the potatoes over the top of the mixture, pour over half the stock, then season.
8 Spread the remaining chicken and onion mixture then carefully layer the remaining potatoes over it. Add the remaining stock then season. There should be three layers of potato and two layers of chicken and onion.
9 Dot some butter over the potatoes, cover with foil and bake for one hour.
10 Remove the foil and put back in the oven for 20-30 minutes until the top is crisp and the potatoes are tender. Serve with a crisp green salad and perhaps some crème fraiche mixed with horseradish for a bit of a kick.