First, you might try even darker chocolate for a lower sugar level. Endangered Species Chocolate's “black panther” chocolate is 88% cacao. Half a bar has 5 grams of sugar, so a quarter would be just 2.5 grams of sugar. read more
But realistically, 72% chocolate is 28% sugar, and it’s a waste of your carbs. Go for a darker one and you have more room to play. My favourite is the Lindt 99% chocolate. read more
Real dark chocolate is one of the best keto treats. It's so potent that if you get the Lindt (or similar brands, shaped bars) one square is plenty for a quick treat and amounts to about 2-3 carbs. Plus you don't have to worry about all the gas and shit brewing sugar alcohols in those nasty tasting "diet" chocolate bars. read more