Add the blueberries, sugar, lemon juice, zest, salt and cornstarch to a medium saucepan. Bring to a boil over medium heat, stirring often for 5-7 minutes or until jam thickens. Stir in vanilla and cinnamon then pour jam into a bowl. Place bowl in the fridge to cool. Jam will continue to thicken as it cools. 

Chop butter into cubes and place in the fridge while you assemble the rest of the ingredients.

Fill a small bowl with some cold water and an ice cube. Stir the ice cube around a bit and set bowl aside.

In a food processor, pulse together the flour, sugar, and salt. Add the cubed butter and pulse until the dough forms pea sized balls. Add ice water a tablespoon at a time while continuing to pulse mixture until it is just combined. 

Divide dough in half. Place each half on a sheet of plastic wrap. Loosely wrap each ball in plastic wrap and gently press each dough ball into a disc shape. Place each disc in the fridge for at least two hours or up to two days. 

Remove the dough from the fridge and let it stand at room temperature for 30 minutes. Keep the other disc in the refrigerator. Prepare and set aside the egg wash.

Roll out one disc of dough on a lightly floured surface. Sprinkle freeze dried blueberries (if using) over the dough as you roll it out. If the dough isn’t rolling out smoothly at first, gently pat it down with your hands. The warmth from your hands will make it easier to work with. Roll the first disk out on your floured counter into a rectangle about 1/8″ thickness and about 9″ x 12″ in size. Trim the sides as needed. Use a ruler to help you measure and cut out 3×4 inch rectangles. You should have 6 or seven rectangles). 

Place the rectangles on a parchment paper lined baking sheet. Place the baking sheet in the fridge. Roll the second disc adding freeze dried blueberries as you roll it out. Sprinkle them over the dough and incorporate them with the rolling pin as you roll the dough out. Roll it out the same size as the other disk and cut dough out into 6-7 even rectangles. 

Remove other baking sheet of rectangles from the refrigerator. Brush egg wash over the whole surface of each rectangle. Place a heaping tablespoon of the blueberry filling into the center of each rectangle. Spread it around, making sure to leave a 1/4 inch of space on the edges. Brush the remaining rectangles (these will be the tops) with egg wash and place each rectangle egg wash side down on top of the rectangles with filling on top. Use your fingertips to press firmly around the filling (this will make sure the filling is sealed inside on all sides). Crimp the edges using the tines of a fork. 

Use a fork or a toothpick to poke holes in the top of each pop tart.  Refrigerate the filled pop-tarts uncovered for at least 20 minutes and up to 1 hour. 

Preheat oven to 350 F. When ready to bake your pop tarts, remove them from the refrigerator and brush tops with egg wash. Bake for about 22-28 minutes (rotate the pans halfway through baking) until golden brown. Let the baked pop tarts cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely before topping them with icing. 

Stir together the powdered sugar, heavy cream or milk, and blueberry jam. Spread or drizzle the icing over the pop tarts!