To make the filling:

1. In a medium sauce pan, add blueberries, lemon zest, lemon juice, and sugar
2. Bring to a boil over medium heat
3. In a small bowl, add cornstarch and water and stir together
4. Add to the blueberry mixture
5. Turn down the heat and simmer for about 10 minutes, stirring often
6. Remove from the heat and allow to cool

To make the crust:

1. Add shredded butter, flour, sugar and salt
2. Work together with a pastry cutter until you have a crumble mixture
3. Add cold water 1 TBSP at a time until you can form a ball
4. Chill for 45 minutes
5. Remove from the fridge and roll out the dough to a 9×12 rectangle
6. Cut into 2.5×4 inch rectangles
7. Add 1 1/2 TBSP of filling and add a second layer of dough
8. Seal with a fork around all edges
9. Poke the top of each pop tart with a fork to vent
10. Place on a baking sheet lined with parchment paper and bake at 400 degrees for 25 minutes
11. Remove from oven and allow to cool completely

To make the icing:

1. With a mixer, add powder sugar, vanilla, and gradually add milk
2. Mix until combined and get desired consistency
3. Top off each cooled pastry with icing and add sprinkles