Blanch the cabbage leaves in a pan of salted boiling water for 10 minutes. Refresh under cold water and drain well to retain their vibrant color and texture.
Slice the chicken breast lengthwise in half and flatten the pieces gently. In a hot frying pan, melt 20g of butter. Season the chicken cutlets with salt and pepper, then sear for 2 minutes per side. Set aside to rest.
In the same pan, sear the foie gras escalopes—seasoned with salt and pepper—for 30 seconds on each side. Allow to cool slightly for easier handling.
Discard excess fat from the pan. Reduce the chicken broth to three-quarters volume. Add the Port and reduce by half. Stir in the remaining butter to emulsify gently, followed by the chopped truffles. Season to taste and keep warm.
Preheat the oven to thermostat 7 (210°C). Beat the egg with a splash of water to create an egg wash.
Roll out the puff pastry and cut into two rectangles. Layer on each: half a cabbage leaf, a chicken cutlet, another half cabbage leaf, and a foie gras slice. Top with the final half cabbage leaf. Brush the dough edges with egg wash, fold over to seal the filling securely.
Moisten a baking sheet and place the pastries on it. Brush the tops with remaining egg wash. Bake for 15 minutes until golden and crisp.
Let rest for 5 minutes, then plate elegantly.
Serve with the warm truffle jus and any reheated leftover cabbage leaves.
