Ingredients
3 tablespoons sugar
2 teaspoons cornstarch
Pinch of kosher salt
5 ounces fresh blueberries (1 cup)
Grated zest of 1/2 lemon
Unbleached all-purpose flour, for dusting
1 package (14 ounces) all-butter puff pastry, thawed
1 large egg
Sugar/Blueberry Glaze (recipe follows) and purple sprinkles (optional), for decorating
1/4 cup freeze-dried blueberries (optional; omit to keep glaze white)
1 1/4 cups confectioners' sugar
1/4 teaspoon pure vanilla extract
Preparation
Stir together sugar, cornstarch, and salt. Add berries and zest; toss to coat, mashing some berries against side of bowl. On a lightly floured surface, roll pastry into a rectangle; cut into six 4-by-5-inch rectangles.
Place 1 heaping tablespoon of filling lengthwise on one half of each rectangle, leaving a 1/2-inch border. Whisk egg with 1 teaspoon water. Brush borders with egg wash; fold dough over filling and press edges to seal. With the tip of a sharp knife, cut vents in each pastry. Arrange pastries on a parchment-lined baking sheet; freeze until firm, 20 minutes (or, wrapped in plastic, up to 2 days).
Preheat oven to 400 degrees. Brush pastries with egg wash. Bake, rotating sheet halfway through, until deep golden brown and juices are bubbling, 25 to 27 minutes. Transfer using parchment to a wire rack; let cool completely. Glaze and decorate as desired. Let set before serving.
Place blueberries in a resealable plastic bag; crush with a rolling pin until finely ground. (You should have 1 tablespoon.) Transfer to a bowl; whisk in sugar. Gradually whisk in 1 tablespoon water and vanilla. Whisk in more water, 1 teaspoon at a time, until thick like honey. Whisk until smooth. Use immediately.
