Agri-tech start-up, Perfect Day, released a line of real ice cream made with lab-grown dairy that costs $20 a pint on Thursday - and it sold out in hours. Perfect Day's cultured dairy is created by taking cow's milk DNA and adding it to a micro-organism like yeast to create dairy proteins, whey and casein, via fermentation. Those dairy proteins are then combined with water and plant-based ingredients to create a dairy substitute that can be used to make ice cream, cheese, yogurt and a slew of other dairy products. [Co-founder Perumal] Gandhi ... says the dairy substitute is nutritionally identical to cow's milk and tastes just like it. In fact, while Perfect Day Foods at least considers its product vegan" and lactose-free (since lactose is a sugar found only in mammals' milk), federal law actually requires them to put "contains milk" on any labeling because its protein is identical to cow's milk on a molecular level and could cause allergies. Co-founder Rayan Pandya, 27, says the process to make the dairy is similar to what plant-based "meat" start-up Impossible Foods is doing using heme, a molecule in soy plants that's identical to the heme molecule found in meat. Using heme, Impossible Foods is able to make its vegetarian meat substitute taste and feel like beef without using animals. The limited edition run of 1,000 three-packs of Perfect Day ice cream ... was the first and only product released by Perfect Day Foods (which has been working with the Food and Drug Administration since 2014) to drum up buzz.