1-First, place the chicken in a bowl with 45 g (6 tbsp) plain flour, ½ tsp salt, and ½ tsp black pepper, tossing to coat well.

2-Next, heat 2 tbsp oil in a large frying pan or skillet over high heat and brown the chicken in two batches until golden but not fully cooked; remove and set aside.

3-Then, in the same pan, melt 2 tbsp unsalted butter over low-medium heat, add 3 small-to-medium onions, 5 cloves garlic, 1 tsp dried thyme, and ½ tsp celery salt if using, and cook for 5 minutes until the onions soften.

4-After that, sprinkle 25 g (3 tbsp) plain flour over the onion mixture and stir for 1 minute.

5-Pour in a splash of 1 litre (4 1/4 cups) chicken stock, whisking to combine and prevent lumps, then gradually add the remaining stock while stirring until a smooth sauce forms.

6-Add 300 ml (1 1/4 cups) whole milk or half-fat and cook until the sauce thickens; stir in 2 tbsp freshly squeezed lemon juice.

7-Now, mix in 20 chestnut mushrooms, the cooked chicken, ½ tsp salt, and ½ tsp pepper, cover with a lid, and simmer gently on the stovetop for 20 minutes.

8-For a baked version, transfer to a casserole dish, cover with foil, and bake at 175°C/350°F for 30 minutes.

9-Finally, remove the lid, stir in 240 ml (1 cup) double cream, and heat through for 5 more minutes, or return to the oven uncovered if baking; if needed, thicken with the optional cornflour slurry.

10-Serve with mashed potatoes, sprouts, peas, and sweetcorn, and sprinkle with the chopped parsley for a fresh finish.