Preheat your Crock-Pot® for 20 minutes on high while you prepare the chicken and vegetables. Season the chicken liberally with salt and pepper.
Heat the butter and olive oil in a large frying pan and sear the chicken for a few minutes on all sides until golden. Season with half the herbs and set aside. Add all the vegetables to the pan and stir for 5 minutes until they start to soften.
Deglaze the pan with the wine and squeeze the lemon over the vegetables. Season the vegetables with salt and pepper and add the remaining herbs. Add the stock and bring to a simmer.
Transfer the vegetables and stock to the Crock-Pot® and then nestle the chicken on top. Add the spent lemon and garlic into the chicken cavity.
Cover with foil, add the lid and cook for 3 hours on high or until the chicken registers internal temperature of 80°C on a digital thermometer. Remove the chicken from the slow cooker and place on a oven tray.
Strain the vegetables and return the stock back into the Crock-Pot® . You can discard the celery and shallots but keep the carrots to serve with the roast.
Arrange the potatoes around the chicken and brown under a hot grill for 5 minutes to crisp up the skin – this is optional. Rest the chicken for 15 minutes.
Add the cornflour slurry to the Crock-Pot® cook on high for 15 minutes while chicken rests (alternatively do this step in a saucepan on your stove top). Serve your chicken with the potatoes and carrots with plenty of gravy!