Blanch the basil in boiling salted water just until wilted, about 10 seconds, then drain and transfer to ice water. Drain again and squeeze dry. Chop roughly. Puree the basil, basil oil, ascorbic acid, and salt in a food processor. If the mixture is too dry to puree, add just enough water to ease the process. Add the butter, in tablespoon-size pieces, and puree until smooth and well blended. Taste and add more salt if desired. Transfer to a bowl and stir in the chives by hand. Refrigerate until firm enough to shape into a log.
Put an 18-inch sheet of aluminum foil on your work surface. Spoon the butter down the center of the sheet into a log about 1-1/2 inches in diameter. Enclose in foil and twist the ends to make a sealed log, like a Tootsie Roll. Refrigerate for up to 1 week, or freeze for up to 6 months.
Slather this emerald green butter on planked salmon, steak, or scallops. Put a spoonful in a shrimp or asparagus risotto, float a slice on corn soup, or spread on toasted pain au levain (sourdough bread) and top with prosciutto. Having these butters in the freezer is a real time-saver; all you need is chicken breasts or some good steaks to make a great meal in minutes. Just unwrap and slice as much butter as you need, then rewrap and refreeze for the next time.