Prepare the chicken: Pat the chicken thighs dry with kitchen paper. Season generously on both sides with salt and black pepper. The skin should feel dry to the touch, which is key for a good sear.

Brown the chicken: Heat the vegetable oil in a large frying pan or skillet over medium-high heat until it shimmers. Place the chicken thighs skin-side down in a single layer. You should hear a vigorous sizzle. Cook for 5-6 minutes without moving them, until the skin is a deep golden brown and releases easily from the pan. Flip and brown the other side for 3-4 minutes. Transfer the chicken to a plate; the kitchen will smell wonderfully savoury.

Sauté the vegetables: Reduce the heat to medium. Add the diced onion and celery to the pan. Stir with a wooden spoon, scraping up any browned bits from the bottom. Cook for 5-6 minutes until the onions become translucent and soft, and you can smell their sweetness. Add the minced garlic and cook for another 30 seconds until fragrant.

Make the roux: Sprinkle the flour over the softened vegetables. Stir constantly for 2-3 minutes. The mixture will look like a thick paste and will begin to smell slightly nutty. Cook until the roux turns a light caramel colour, about the shade of a brown paper bag.

Build the gravy: Slowly pour in the warmed chicken stock while whisking continuously to prevent lumps. The mixture will steam and thicken almost immediately. Add the dried thyme, smoked paprika, and the bay leaf. Bring the gravy to a gentle simmer; you will see small bubbles breaking the surface. Taste and adjust seasoning with salt and pepper.

Smother the chicken: Return the browned chicken thighs to the pan, skin-side up, nestling them into the gravy. The liquid should come about halfway up the sides of the chicken. Reduce the heat to low, cover the pan with a lid, and let it simmer gently for 30 minutes. The gravy will bubble softly, and the chicken will become incredibly tender.

Finish and serve: After 30 minutes, remove the lid and increase the heat slightly to medium-low. Simmer uncovered for a final 5-10 minutes to allow the gravy to thicken to a coating consistency. The chicken should be so tender it nearly falls off the bone. Remove the bay leaf, garnish with fresh parsley, and serve immediately.