Remove the core of the apple (the pips) using an apple corer then cut it into thin slices.
Toast the walnut kernels.
In a container, stir the saffron with a teaspoon (5 ml) of boiling water. Let stand 2 minutes until the pistils are softened.
Mix the previous infusion, champagne vinegar, mustard and sugar.
Whisking continuously, drizzle in the olive oil to emulsify the vinaigrette.
Season with salt and pepper to taste.
Dress the salad by alternating the endive leaves and the apple slices. Add the walnut kernels.
Serve the sauce in a sauce boat.
