Ingredients
1 lb fresh or frozen blueberries (3 cups)
2 tablespoons cornstarch
1 tablespoon finely grated fresh lemon zest
1 tablespoon fresh lemon juice
1/4 teaspoon ground cinnamon
1/4 teaspoon salt
1/2 cup plus 1 teaspoon sugar
1 puff pastry sheet (if bought frozen, thawed of course)
1 tablespoon cold unsalted butter, cut into pieces
1 large egg, lightly beaten
Directions
Stir together blueberries, cornstarch, zest, juice, cinnamon, salt, and 1/2 cup sugar in a large bowl until combined.
Unwrap puff pastry and unfold onto baking sheet. You can leave it square or cut the corners into a circle (to your preference). Dock the pastry with a fork a few times, all the way to the edges.
Spoon blueberry mixture onto center of dough, leaving a 1 1/2-inch border around edge. Fold edge of dough over 1 inch of blueberry mixture, pleating dough, then dot blueberry filling with butter pieces. Lightly brush pastry with some of beaten egg and sprinkle with remaining teaspoon sugar.
Bake until blueberry filling is bubbling and pastry is golden, 25 to 30 minutes. Cool slightly on baking sheet on a rack. Serve warm.
