In a 3-qt heavy-duty saucepan, combine the condensed milk, cream, 6 tbs ground pistachios, corn syrup and butter and bring to a boil over medium heat. Reduce the heat to medium-low and continue to cook, stirring constantly with a whisk, until the mixture thickens and starts to form a dense batter. This will take about 12 minutes. When the mixture is properly cooked, the whisk will leave trails in the batter that briefly expose the bottom of the pan, and the mixture will slide to the side in a blob when the pan is tilted, leaving a thick residue on the bottom of the pan.
Slide the mixture into a bowl, but do not scrape the pan -- you don't want to use the residue that's stuck to the pan, or your candies will be gritty and off-textured. Allow the mixture to cool to room temp, then chill for about 3 to 4 hours, or until mixture is very firm.
Put the remaining ground pistachios (you should have 1/4 cup left) in a bowl. Using a small cookie scoop, portion out the mixture and roll by hand into balls that are approximately 1" in diameter. Drop each rolled ball into the pistachios and toss to coat. Remove the coated candies from the pistachios, allowing the excess nuts to sift through your fingers, and place the candies in tiny paper candy cups. If you find that the nuts are not sticking well to the outside of the candies, you can roll them around a bit more in your hands before coating (this warms them up a bit so they soften).
These can be stored tightly covered at room temperature If you choose to refrigerate them for storage, allow them to come to room temp before serving for best flavor.