First, complete Lily's request to have some start up money for this to work and make sure someone is selling items at the bar--preferably Lily or Electra, for the access to Ice Cream:
1. Purchase all the milk you can.for 120g 2. Cook it into Hot Milk at the inn's kitchen. 3. Sell it back to the store for 200g. 4. Buy Ice Cream as needed to replenish RP. Rinse and repeat until you are satisfied or bored.