Preheat oven to 200°C fan-forced. Brine the chicken thighs in 1L of cold water mixed with 30g of salt for 30 minutes. Drain and pat very dry.
Heat the olive oil in a wide cast-iron pan over medium-high. Season the chicken with pepper. Place skin-side-down in the pan.
Brown for 6 minutes without moving, until the skin is deep mahogany. Flip the thighs.
Whisk the marmalade, soy, mustard, wine, garlic and pepper in a small bowl until pourable. Brush half over the chicken skin.
Tuck the thyme sprigs and orange rounds between the thighs. Transfer the pan to the oven.
Bake 15 minutes. Brush with the remaining glaze. Bake another 10 minutes until the skin is glossy mahogany and the juices run clear when a thigh is pierced at the bone.
Rest 5 minutes in the pan. Sprinkle with flaky salt. Serve with the pan juices spooned over, on a generous puddle of mash, polenta or steamed rice.