Care to milk your own milk? Two shares in a Jersey cow are up for purchase in Nicasio, where four-year-old Rosy Belle offers her milk to a handful of families who co-own her. “It’s like a tiny cooperative or partnership,” said Eleanor Despina, who bought Rosy from rancher John Taverna in January—along with Nicasio resident Marnie Jackson, who keeps the cow on her property, and eight other families. While pasteurization removes potentially harmful bacteria, it…