Peel and pit the chayotes, slice them thinly, and simmer in lightly salted boiling water for 10 minutes. Drain thoroughly to ensure a non-watery gratin.
Lightly grease a gratin dish and arrange the chayote slices inside.
Peel and finely chop the shallot, then scatter it evenly over the chayotes.
Whisk the thick cream with the whole egg until smooth and well combined.
Preheat your oven to 200°C.
Sprinkle Guérande fleur de sel and lightly crushed Sichuan pepper over the chayotes for balanced seasoning.
Generously top with grated Emmental cheese.
Bake until the surface turns golden brown and crispy, about 20 minutes.
Serve hot for optimal flavor and texture.
