Make the Dough:

In a large bowl, whisk together the flour, sugar, salt, and cinnamon.

Cut in the cold butter using a pastry cutter or your fingertips until the mixture resembles coarse crumbs with pea-sized pieces of butter.

Gradually add the ice water, 1 tablespoon at a time, mixing just until the dough comes together.

Divide the dough into two equal portions, flatten each into a disk, wrap tightly, and refrigerate for at least 1 hour. Keeping the dough cold helps create a flaky pastry.

Make the Filling:

In a small saucepan, combine the strawberries, sugar, lemon juice, lemon zest, and vanilla.

Cook over medium heat until the strawberries begin to break down.

Stir together the cornstarch and water, then add it to the saucepan.

Continue cooking for 2–3 minutes, stirring frequently, until the filling thickens to a jam-like consistency.

Transfer to a bowl and let it cool completely before assembling.

Assemble the Pop-Tarts:

Preheat the oven to 375°F. Line a baking sheet with parchment paper.

Roll each dough disk into a rectangle about ⅛-inch thick.

Cut into 3x4-inch rectangles.

Place half of the rectangles on the prepared baking sheet.

Spoon about 1–2 tablespoons of the cooled strawberry filling into the center of each, leaving a ½-inch border around the edges.

Brush the edges lightly with water, then place another rectangle on top.

Press around the edges to seal, then crimp with a fork.

Use a fork to poke a few holes in the tops to allow steam to escape while baking. Docking the tops helps prevent the pastries from puffing excessively.

Brush the tops with the beaten egg.

Bake:

Bake for 25–30 minutes, or until the pastries are lightly golden.

Transfer to a wire rack and let them cool completely.

Glaze:

Whisk together the powdered sugar, milk, vanilla, and freeze-dried strawberry powder (if using) until smooth.

Spread the glaze over the cooled pastries and immediately decorate with sprinkles if desired.

Let the glaze set before serving.