Wipe the chicken thighs with paper towels.
Using a heavy knife, chop each thigh through the bone into two portions.
Toss the chicken thighs with a teaspoon of salt and half a teaspoon of pepper.
Heat the cooking oil in a wok or casserole.
Over high heat, spread the chicken in hot oil and allow the undersides to sear for a few minutes. Flip and sear the opposite sides. Stir and continue cooking until the chicken is lightly browned on all sides.
Scoop out the chicken and transfer to a plate.
In the remaining oil (which now includes rendered fat from the chicken skin), soften the onion slices with a little salt and pepper over medium heat.
Add the garlic and ginger. Sprinkle in a bit more salt and pepper. Continue cooking, stirring often, for a minute or two.
Throw in the carrot cubes and cook with occasional stirring for a minute.
Stir in the chicken.
Pour in the broth. Bring to the boill, lower the heat and cover the pan. Cook for 10 minutes.
Stir in the potato cubes. Cover the pan again and cook for 15 to 20 minutes or until both the carrot and potato cubes are cooked through.
Grate the apple dirctly into the pan and stir.
Add the roux, a heaping tablespoonful at a time and stirring after each addition. When all of the roux has been added, simmer the chicken curry for another 10 minutes.
Taste the sauce and adjust the seasonings, as needed.
Scoop rice into shallow bowls and ladle the chicken curry around the rice.