Coarsely pound the salt into small granules in a mortar and pestle. Alternatively just use a small pinch of regular table salt.
Rinse the berries (frozen ones need rinsing too) and add to a small saucepan. Stir in the chia seeds. Add ½ cup water and cook covered over a medium heat for 7 mins.
Take the pan off the heat and let it sit covered for 10 mins. If the mixture appears too dry at this stage, stir in a few teaspoons of water. You want it thick but spreadable. Place in the fridge to cool.
Break up the chocolate into small pieces and add to a bowl. Microwave the chocolate in 1 minute bursts, stirring between each, until melted. Set aside to cool.
Line a baking tray with parchment/foil. Place the dates in an approximate rectangular shape on the tray. Place another layer of parchment/foil on top.
Press the dates down with your fingers/knuckles until they flatten and spread out. Carefully remove the top layer of parchment.
Spread the peanut butter evenly over the dates. Next spread the blueberry-chia evenly over the peanut butter. Pour over the melted chocolate and nudge them to the edges to get an even layer. Sprinkle over the salt.
Freeze the tray for 15 mins, then slice into uneven squares. To store keep them in a covered container in the fridge.