Preheat and prepare the pan. Set your oven to 180°C (160°C fan) or 350°F. Place the sliced onion in an even layer across the bottom of a 9x13 inch baking dish. The onions will soften and sweeten as they cook, forming a fragrant bed for the chicken.

Make the honey mustard glaze. In a mixing bowl, combine the clear honey, whole grain mustard, Dijon mustard, olive oil, minced garlic, softened butter, apple cider vinegar, smoked paprika, dried thyme, salt, and pepper. Whisk until the butter is fully incorporated and you have a thick, glossy, golden-brown paste. Smell it — the sharpness of the mustard should cut through the sweetness of the honey beautifully.

Prepare the chicken. Pat the chicken thighs dry with kitchen paper. This step is crucial for achieving crispy skin. Place the thighs skin-side up on a cutting board and, using your fingers, gently loosen the skin from the meat, creating a small pocket. Spoon about a teaspoon of the glaze under the skin of each thigh, spreading it directly onto the flesh. The skin will protect the meat and keep it incredibly moist.

Arrange and coat. Place the chicken thighs skin-side up on top of the sliced onions. Using a pastry brush, generously brush the remaining glaze all over the top and sides of the chicken. The skin should look well coated and glossy. Pour the chicken stock around the edges of the dish, being careful not to wash the glaze off the chicken. The stock will steam and keep everything moist.

First bake. Place the dish in the preheated oven, uncovered, and bake for 35 minutes. At this point, the kitchen will be filled with a rich, sweet-savoury aroma. The chicken will be partially cooked, and the skin will be starting to turn a pale golden colour.

Baste and continue. Remove the dish from the oven and carefully baste the chicken with the pan juices. The liquid should have reduced slightly and look syrupy. Return the dish to the oven for another 20-25 minutes. The skin will deepen to a rich mahogany brown, and the edges will begin to caramelise and crisp.

Check for doneness. The chicken is ready when the skin is crackling and deep golden-brown, the juices run clear when pierced with a skewer at the thickest part, and an internal thermometer reads 75°C. The onions should be soft and jammy, swimming in a glossy, thickened sauce. The sound of the pan as you pull it out should be a gentle, sticky sizzle.

Rest and serve. Allow the chicken to rest in the dish for 5-10 minutes before serving. This lets the juices redistribute throughout the meat, ensuring every bite is succulent. Spoon the onions and pan sauce over the chicken as you plate it.