In the bowl of a food processor, pulse together the flour and salt. Cut the butter into tablespoon pieces and add half on top of the flour mixture. Pulse 5-6 times and add the remaining butter. Pulse in short bursts until pea-sized pieces are scattered throughout the flour. Add ice cold water 1 tablespoon at a time through the feed tube while processing in short bursts. Keep pulsing until a shaggy ball is formed to one side of the bowl.

Turn out the dough and shape into a ball. Cut in half. Roll each piece of dough on a piece of floured parchment paper to about 14×10 inches. Trim each piece to 13×9 inches using a large chef’s knife. Stack the dough between parchment paper and transfer on a baking sheet to the refrigerator. Chill while you make the strawberry filling.

Place the strawberries, sugar, and lemon juice in a medium saucepan. Cook over medium high heat until the berries give off their juices and start to lose their shape. Keep stirring until some of the liquid is cooked off and the mixture is slightly syrupy, about 10 minutes. The berries should be almost translucent.

In a small cup, stir the cornstarch into the water. Immediately add the mixture to the berries while whisking constantly. Cook an additional 1-2 minutes, or until the mixture thickens. Stir in the salt and vanilla extract. Remove from the stove top and let cool 10 minutes. Pour into a shallow dish and transfer to the refrigerator to cool completely, about 30 minutes.

Beat the egg and the water together in a small bowl.

Preheat the oven to 375F.

Remove the pie crusts from the refrigerator. Place one on a large parchment-lined baking sheet. Cover the crust with the cooled strawberry jam within 1 ½ inches of the edge. Brush the edge of the pastry with the egg wash. Top with the second pie crust, lining up the edges evenly.

Use a fork to crimp the edges of the pastry. Use the fork tines to poke holes all over the top crust. Lightly brush the entire surface of the pastry with the egg wash.

Bake the pastry for 20 minutes. The pop tart will puff up like a pillow as it bakes. Remove the pastry from the oven and allow it to deflate. Preheat the broiler. Place the pop tart under the broiler for 2-3 minutes, or until the surface is golden brown.

Allow the pastry to cool on the pan for 5 minutes, then slide it onto a wire rack to cool completely.

Whisk together the confectioners’ sugar and vanilla. Add additional milk, if needed to thin the mixture. It should be thick and opaque yet still pourable.

Pour the mixture on top of the cooled pop tart. Top with rainbow sprinkles. Allow the glaze to crust, about 5 minutes.

To serve, cut into 12 squares (more or less to suit your appetite!).