Herman is not available at stores. You need to get him from a friend. It works via a fermentation process of 10 days. On day 4, you have to add sugar, flower and milk. On day 9, you add that same amount of ingredients again, and divide the dough in 5 portions. You have to give 4 of them to friends, who will follow the same steps and preserve the chain. You keep the 5th portion for yourself, add more ingredients on the 10th day and put Herman in the oven.
Ceterum censeo OTF esse delendam.