Instructions
Buy a chili seed, a gooseberry seed and some milk from the general store. Plant the two seeds in your garden.
Visit Bart after your gardening skill has reached at least level four. Give him the milk to tinker with, and he will turn it into cheese. Visit Bart again and have him tinker with the cheese; he will turn it into a cheesecake.
Wait until the plants produce at least three gooseberries and two chilies. Sooner or later, a Rashberry will appear. Once it has eaten two gooseberries and two chilies, it will become a resident of your garden.
Feed the Rashberry the cheesecake, and it will evolve into a Hoghurt warthog.