Add the berries, 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 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. Take the blade out of the food processor and add sprinkles. Alternatively, sprinkles can be added after cutting the dough out in a later step. 

Turn the dough out onto a sheet of plastic wrap. Loosely wrap the ball of dough in plastic wrap and gently press to shape the dough into a disk shape. Place the disk in the fridge for at least two hours or up to two days.

When ready to assemble pop tart, remove the dough from the fridge and let it stand at room temperature for 15 minutes. Line a baking sheet with parchment paper, generously flour your counter, and prepare your egg wash by whisking together the egg and milk. Set aside. 

Roll the first disk out on your floured counter to about 1/8" thickness. 

Lightly flour your 3" cookie cutter or biscuit cutter and cut out circles. Place the circles on your baking sheets. Scraps can be rolled out/cut out a second time. 

Brush the edges of the bottom layer with the egg wash. Spoon a rounded teaspoon of  jam and a few bits of chopped strawberries onto the crust and spread it with the back of your spoon or an offset spatula, leaving a 1/4 inch border.  Carefully place a top circle over the bottom crust. Gently press the edges of the dough with your finger tips to seal the top and bottom crusts together. Use a fork to crimp all the edges. (Lightly dip fork in flour if needed to prevent sticking). Use a fork or a toothpick to poke a few holes in the dough and place in the fridge for 30 minutes. Preheat oven to 375 F.

Remove dough from fridge and brush the tops allover with the egg wash. Bake for 15-17 minutes or until golden brown, rotating pan halfway through cooking. Remove from heat and transfer to a rack to cool. Serve with a drizzle of icing, with a scoop of ice cream or enjoy as is! 

Stir together the powdered sugar, heavy cream, milk, and vanilla. Drizzle over the pop tarts!