Remove the stems and finely chop the strawberries if using fresh ones.

Combine strawberries, sugar, and lemon juice in a medium pot.

Cook over medium heat until the sugar dissolves.

Increase the heat to high and boil for 1 to 2 minutes, stirring occasionally.

Reduce the heat to medium and simmer for about 10 minutes, until thick. Transfer the mixture to a glass jar and let it cool.

Extra preserves can be stored in the fridge for up to 2 weeks.

Preheat the oven to 350°F (175°C) and line a baking sheet with parchment paper.

In a mixing bowl, stir the softened butter, sugars, and vanilla extract until combined.

In a separate small bowl, mix the sourdough discard and egg yolk.

Add flour to the butter mixture and then the egg yolk mixture. Mix on low until crumbly, adding water as needed until the dough comes together.

Form it into a smooth ball with your hands.

On a floured surface or parchment paper, roll out the dough into a 14-inch square, about 1/8-inch to 1/4-inch thick.

Trim the edges to make a 12-inch rectangle and cut out twelve 4 by 3-inch rectangles.

Place half of the rectangles on the prepared baking sheet.

Mix the strawberry preserves and cornstarch in a bowl.

Spoon about 1 tablespoon of filling into the center of each dough rectangle.

Dab water around the edges to help seal. Top each rectangle with another piece of dough.

Use a fork to crimp the edges and poke holes in the top to allow steam to escape.

Bake for 20 to 25 minutes or until the bottoms are lightly golden brown.

Allow them to cool completely on the baking sheet.

In a small bowl, whisk together the powdered sugar and milk until smooth and thick.

Frost each pop tart with the glaze and sprinkle with natural decorating sugars.