Remove stems and finely chop fresh strawberries. If using frozen, thaw and drain excess liquid first.

Combine strawberries, 57 g cane sugar, and 1/2 tsp lemon juice in a medium pot.

Heat over medium until the sugar dissolves.

Increase heat to high and boil 1–2 minutes, stirring. If using frozen berries, boil an extra minute or two.

Reduce to medium and simmer about 10 minutes until fruit breaks down and thickens.

Transfer to a glass jar and cool to room temperature. Refrigerate extras up to 2 weeks.

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

In a bowl, stir 57 g softened butter, 57 g cane sugar, 35 g powdered sugar, and 1 tsp vanilla until smooth and no butter lumps remain.

In a small bowl, whisk 57 g sourdough discard and 1 egg yolk.

Add 255 g flour and 1/4 tsp salt to the butter mixture. Pour the egg-yolk mixture on top and mix on low until crumbly.

Add water 1 tsp at a time (about 2 tbsp total) until the dough just comes together.

Bring dough together with your hands into a cohesive ball.

On a floured surface or piece of parchment, roll dough into a 14-inch square about 1/8–1/4 inch thick.

Trim to a 12-inch rectangle. Cut twelve 4 x 3-inch rectangles.

Place 6 rectangles on the prepared baking sheet.

In a small bowl, mix 88 g cooled strawberry preserves with 1 tsp cornstarch. Add 2–3 tbsp water only if needed to loosen slightly—aim for a spoonable jam.

Spoon ~1 tablespoon of filling into the center of each bottom rectangle.

Lightly brush water around the edges of each filled rectangle. Top with the remaining rectangles.

Crimp edges with a fork. Poke holes all over the top or make two slits for steam to escape.

Bake for 20–25 minutes, or until the bottoms’ edges are lightly golden.

Cool completely on the baking sheet.

Whisk 106 g sifted powdered sugar with 1–2 tbsp milk until a thick, spreadable glaze forms.

Frost each cooled pop tart and sprinkle natural decorating sugars.

Store in an airtight container for up to 3 days.