The winter solstice is the darkest night of the year. Salt & Straw aims to also make it one of the sweetest. The Portland-based ice cream chain announced a free upgrade for customers visiting any of its shops on Saturday, Dec. 21, when the sun will set earlier and rise later than any other time of year. All single scoops will get doubled at no cost, while gift cards of $25 and higher will get a $5 balance boost. The ice cream bonus is a same-day in-person event, while the gift card promotion runs in stores and online through the end of the year.