Combine frozen berries and sugar in a saucepan and heat over medium.  As the sugar dissolves and the berries begin to release their juices, use a potato masher or the back of a fork to help the berries break down.  Continue to cook over medium-low, stirring and mashing frequently, until the berries have broken down and the mixture is syrupy, about 7-10 minutes.  Transfer to a fine mesh strainer set over a bowl and strain, pressing down with a rubber spatula to make sure to get as much of the berry syrup while leaving the seeds and skins behind.  Discard the seeds and skins in the strainer.

Add remaining ½ cup of sugar to the warm berry syrup and whisk until the sugar has completely dissolved.  Whisk in skyr, cream, vanilla and salt until the mixture is completely smooth.  Cover and chill the mixture until it is very cold, at least three hours.  Churn according to manufacturer’s instructions in an ice cream machine.

Either enjoy immediately (frozen yogurt will be a soft-serve texture at this point), or transfer to a freezer-safe, sealed container and freeze until firm before serving.  If frozen skyr is too firm to scoop, set out at room temperature for 15-20 minutes before serving.