For the potato espuma, boil potatoes in salted water until soft and strain, then pass through a sieve.
Boil milk and potato water with butter and spices and stir into the potato mixture.
Pour the still hot, smooth, slightly liquid amount into the iSi-Whip and fill it with two gas capsules, shake the iSi-Whip well three times each. Serve the earth apple espuma with meat or fish.