In a small saucepan, whisk together 1 cup pomegranate juice and 2 tbsp granulated sugar. In a separate small bowl, dissolve 1 tbsp cornstarch in 1–2 Tbsp of water to make a slurry.
1 cup pomegranate juice, 2 tbsp granulated sugar, 1 tbsp cornstarch
Bring the pomegranate juice to a simmer over medium heat, then whisk in the cornstarch slurry. Cook for 2–3 minutes, stirring constantly, until the mixture thickens. Remove from heat, stir in 1 tsp lemon juice, and let cool completely.
1 cup pomegranate juice, 1 tsp lemon juice
Preheat oven to 400°F and line a baking sheet with parchment paper.
Roll out the 1 sheet puff pastry slightly on a lightly floured surface. Spread the cooled pomegranate filling evenly over the puff pastry, leaving a small border around the edges.
1 sheet puff pastry
Starting from one edge, carefully roll the pastry into a tight log. Slice the log into 1-inch thick pinwheels and place them cut-side up on the prepared baking sheet.
Brush the tops lightly with the beaten 1 egg.
1 egg
Bake for 15–18 minutes, or until the pinwheels are golden brown and puffed. Let cool slightly before serving.