Prepare the couscous according to the instructions on the packet, place in a bowl with the parsley, lemon zest and grapes. Whisk the egg with 3/4 of the butter, lemon juice, mustard and pepper, add and mix everything well.
Fill the washed chicken with this mixture, brush with the remaining butter and rub with paprika. Put on a wire rack in the oven, place a drip pan underneath and fry for about 1.5 hours.
Sauce:
Mix the flour with 3 tablespoons of frying fat in a saucepan, brown lightly, pour in the wine and broth and bring to the boil, stirring constantly. Add the grapes and pepper and simmer for 15 minutes. Stir in the cream just before serving.
Slice the chicken and serve with the filling and sauce.