Brown the Chicken: Heat the olive oil in a large, heavy-based frying pan or casserole dish over a medium-high heat. Season the chicken chunks with salt and pepper. Working in two batches to avoid overcrowding the pan, brown the chicken on all sides for 5-7 minutes until golden. Transfer the browned chicken to the slow cooker pot.

Sauté the Vegetables: Lower the heat to medium and add the chopped onions, celery, carrots, and parsnips to the same pan. Cook for 8-10 minutes, stirring occasionally, until the vegetables have softened and the onions are translucent. Add the crushed garlic and cook for another minute until fragrant.

Create the Roux: Sprinkle the plain flour over the vegetables and stir continuously for one minute. This cooks out the raw flour taste and will help to thicken our stew later on.

Deglaze the Pan: If using, pour in the white wine to deglaze the pan. Use a wooden spoon to scrape all the flavourful brown bits from the bottom of the pan. Let it bubble away for a minute or two until the alcohol has mostly evaporated. This is where so much flavour lives! You can learn more about the science behind this browning at Wikipedia.

Build the Gravy: Gradually pour in the hot chicken stock, stirring constantly to create a smooth, lump-free sauce. Stir in the tomato purée and Worcestershire sauce. Bring the mixture to a gentle simmer.

Transfer to Slow Cooker: Carefully pour the vegetable and gravy mixture over the chicken in the slow cooker pot. Add the bay leaves and fresh thyme sprigs. Give everything a good stir to combine.

Slow Cook: Secure the lid and cook on LOW for 7-8 hours or on HIGH for 4 hours, until the chicken is fall-apart tender and the vegetables are soft.

Finish and Serve: Before serving, remove the bay leaves and thyme sprigs. Check the seasoning and add more salt and pepper if needed. I find that a final stir helps to thicken the gravy as the chicken breaks up slightly. Serve hot, sprinkled with fresh chopped parsley.