Ross Warren thought he had merely found the perfect Christmas gift. Every year he’d make just enough jam to give away to family and friends. Then his sister called, telling him that the spread had too much potential to just be a hobby. Soon after, Warren loaded his car with a bunch of jars and sold them to a variety of small grocers in his home state Vermont. He sold out. “I told my wife there’s good news and bad news. Good news is, we sold out. Bad news is, we need 250 more jars. I got to get jamming,” Warren said. That…