Combine the soaked cashews, water, agave, vanilla, and sea salt in a high speed blender. If you are using a Vitamix or high-speed blender simply select variable 1 (the lowest setting), start the machine and slowly increase the speed to variable 10 (the highest setting). Blend for 2 minutes. No straining necessary.
If you are not using a high-speed blender you will need to add a minute to the blend time and possibly strain your cashew milk through a nut milk bag , cheesecloth, or a fine mesh strainer.
Make the blueberry filling
Combine the blueberries, caster sugar, vanilla, and 1/2 cup of the prepared cashew milk in your blender and blend until everything is combined and slightly chunky.
Make your popsicles
Fill your popsicle molds half way with cashew milk then add the blueberry puree until your molds are full. Place the mold in the freezer for about 1 hour and then insert the wooden popsicle sticks into the pops. Return to the freezer for another 4-6 hours until frozen solid.