Place the rack in the middle of the oven. Preheat to 375°F Put parchment paper on a baking sheet.
Roasted Chicken: In a bowl, mix marmalade, butter, parsley and dijon mustard. Add salt and pepper. Set aside.
On a working plan, with a chief knife, cut the bone in the back of the chicken to open it flat. Delicately loosen the skin of the breasts and thighs without breaking it. Spread the mixture of marmalade between the meat and skin. Put the chicken on the baking sheet, breasts side up Add salt and pepper.
Cook in oven 1h15 to 1h30 or until thermometer inserted in the thigh, without touching the bone, shows 82 C (180 F). Baste with the baking juice at mid-cooking. Set aside the chicken and baking juice for the sauce and keep warm.
Orange Sauce: Meanwhile, in a small saucepan, melt butter. Sprinkle with flour and cook 1 minute while stirring. Add orange juice and chicken stock. Bring to boil while stirring with a whisk. Let simmer 2 to 3 minutes. Add baking juice of the chicken. Adjust seasoning.