2 tart green apples, such as Granny Smith, peeled, cored
4 medium potatoes, peeled
salt and freshly ground black pepper
2 tbsp vegetable oil
50²µ/1¾´Ç³ú butter
75²µ/2½´Ç³ú crème fraîche
4 free-range eggs, plus 4 free-range egg yolks
12 thick slices smoked back bacon