Preheat the oven to 400°.
On a flat surface such as a countertop or cutting board, lay out your piecrust. Lightly sprinkle some flour onto the crust and roll with the rolling pin to thin the crust slightly.
Cut the dough into 3"x5" rectangles. Knead the remaining pie crust, and use the rolling pin to make more 3 x 5 rectangles. Place half of the rectangles on a baking sheet or two.
Place about 1 ½ tablespoons of the cooled jam in the center of a half of the rectangles.
Brush ’egg’ wash (aquafaba) and line the sides surrounding the rim.
Take another plain rectangle and place it on top of that rectangle, with the jam, matching the edges.
Use the back of a fork to press the sides to seal in your jam.
Use the ‘egg’ wash (aquafaba) to completely coat the top part of your tart. Use a fork to puncture holes in the top of the tart to allow air to be released while baking.
Place the baking sheets in the preheated oven, and bake for 12 to 15 minutes.
While your tarts are baking in the oven, make your icing. Mix all of the ingredients for the icing and then set aside.
Once your tarts have finished cooking, remove them from the oven and transferred to a cooling rack.
Allow them to cool completely before putting icing on them.
You can choose to put one or more layers of icing on your tart but allow the icing to cool and harden a bit before you add any more.