Prepare Filling

1. Remove stems and chop your strawberries. Add to a saucepan with sugar, cornstarch, and lemon juice.
2. Bring mixture to a simmer, and cook for about 10 minutes, until berries are nice and soft. Use a potato masher or a fork to mash until mostly smooth. You could also use an immersion blender if you want it completely smooth.
3. Cook for about 10 more minutes until mixture is nice and thick. Remove from heat and let it cool.
4. Place in the fridge for at least 60 minutes or until cold.

Prepare Crust

1. Add flour, sugar, and salt to a food processor. Pulse a couple of times just to get the ingredients blended.
2. Add cubes of butter and process until it is crumbly.
3. Slowly pour in the cold water and process until it forms a nice dough.
4. Remove dough from the food processor and use your hands to just shape it into a smooth ball. Flatten slightly into a dish, cover with plastic wrap, and place in the fridge for at least 30 minutes.

Assemble Pop Tarts

1. Once dough is chilled, remove it from the fridge and cut it in half, so you have 2 pieces about the same size.
2. On a well-floured surface roll each ball until about a 12x9-inch rectangle.
3. Cut rectangles that are about 3x4 inches in size using a sharp knife or pizza cutter. Repeat with next pieces of dough. You can combine scraps to roll dough out one more time. In total, you should have 24 3x4 pieces of dough.
4. Using a toothpick or bamboo skewers poke holes in top of half of rectangles. This will allow steam to escape while cooking.
5. Place another half of the rectangles on a lined baking sheet, and fill with strawberry jelly. You will use about two tablespoons of filling per pop tart.
6. Beat together egg and milk for egg wash and gently brush edges of dough.
7. Top each pop tart with remaining rectangles, and gently press down on edges to seal. Use a fork to crimp edges.
8. Brush top with remaining egg wash and bake for 18-22 minutes until they are nice and golden brown.
9. Remove and let cool completely.
10. Adding glaze is optional. Just mix together powdered sugar and milk to get a spreadable consistency. Spread on a cooled pop tart if desired.