Bring 500 ml broth (preferably chicken broth) to a boil in a saucepan. Add 250 g uncooked rice and stir. Reduce heat to low, cover, and simmer for 30 minutes until the rice is tender and the broth is completely absorbed.
While the rice cooks, cut the orange into wedges, then cut each wedge into roughly 3 pieces and set aside.
Pat the chicken fillets dry and season both sides with salt and pepper.
In a shallow bowl, mix 10 tablespoons flour with salt and pepper. In another shallow bowl, beat 2 eggs. In a third shallow bowl, mix 10 tablespoons breadcrumbs with 10 tablespoons chopped hazelnuts.
Coat each chicken fillet by dredging in the flour mixture (shake off excess), dipping in beaten egg, then pressing firmly into the hazelnut mixture on both sides.
Heat 70 g butter in a non-stick frying pan over medium heat. Once foaming, add the coated chicken fillets and fry for 10 minutes on each side until the coating is golden brown and the thickest part of the chicken reaches 74°C (165°F) internally.
While the chicken cooks, heat 30 g butter or margarine in a separate pan over medium heat. Add the finely diced onion and cook for 3 minutes until softened.
Sprinkle 1 tablespoon curry powder and 2 tablespoons flour over the onion, stir, and cook for 1 minute.
Pour in 300 ml whipped cream, stir well, and simmer gently for 2 minutes until slightly thickened. Season to taste with lemon juice, salt, pepper, and a pinch of sugar.
When the rice is cooked and the broth is absorbed, gently fold the orange pieces into the rice.
Serve the chicken fillets with the orange rice on the side (not on top of the meat) and the sauce served separately.