Season the chicken breasts with salt, bell pepper and paprika. Fry in the hot clarified butter on both sides for a total of 2 1/2 to 3 minutes, not too hot. Remove from the frying pan.
Extinguish the pan juices with white wine. Set aside.
In a small frying pan, melt the butter. Add the flour and sauté briefly while stirring. Add the soup and the gravy and let it bubble up. Add the cream and make the sauce, stirring occasionally, for four to five minutes.
In the meantime, finely grate the Gruyère. Set aside a third of the cheese. Mix the remaining Gruyère into the sauce and season it with salt, pepper and a pinch of nutmeg.
Cut the chicken breasts diagonally into slices, then put them together again, but slightly fanned out, in a baking dish.
Spread the cheese sauce evenly over the top. Sprinkle with the remaining cheese.
Up to this point, the dish can be prepared.
Bake the chicken breasts in the oven heated to 220 °C on the second rack from the bottom for twelve minutes.
In the meantime, remove the peel from the garlic and slice it. Pluck the sage leaves from the branches. Roast both in the hot clarified butter until crispy. Sprinkle over the chicken gratin before serving.
Tip: Instead of clarified butter, you can also use butter in most cases.