For the Calvados cream, peel and finely dice the shallots. Heat the butter and sauté the shallots until golden. Deglaze with Calvados and boil down briefly. Add the beef stock and the whipping cream, bring to the boil.
Let it boil down for about 5 minutes, then blend the sauce with a hand blender and season to taste with salt and pepper.
For the steaks au gratin, preheat oven to 220 °C. Sear the steaks in a pan in hot oil on both sides, season with salt and pepper. Put them on a baking tray.
Core the apple, then cut crosswise into thin slices. Cut the Saint Albray into slices. Top the steaks with apple and Saint Albray. Spread the sage leaves on top.
Put the tray in the oven and bake the steaks for about 5 minutes until the cheese has melted.
Warm up the sauce and add the Calvados cream to the steaks. Serve the steaks au gratin with Calvados cream immediately.