This sunshiny tart looks super-impressive but doesn't require any special equipment or pans. Folded foil helps hold up the buttery star-shaped shortbread. The yellow filling is a tangy lemon curd and plump blueberries fill in the edges.
For the shortbread crust: Position an oven rack in the bottom third of the oven and preheat the oven to 350 degrees F.
Combine the flour, butter, confectioners' sugar and salt in a food processor. Pulse until the mixture resembles coarse meal with some pea-sized pieces. Add the egg and pulse until the dough comes together, about 1 minute. Remove 1/3 cup of the dough and set aside. Press the remaining dough into the bottom and up the sides of a 9-inch tart pan. Prick the dough all over with a fork.
To form the star, start by folding a 40-inch-long-by-2 1/2-inch-wide piece of foil into an accordion (there should be about 24 folds, each 1 1/2-inches long); this will become the support for forming your star inside the tart pan. Let the foil open like an accordion and place it in the tart pan in a circle; connect and overlap the end points so that you have an 11-point star.
Roll the reserved 1/3 cup dough into a 27-inch-long rope. Use a rolling pin to flatten the rope into a 34-inch-long-by-1-inch wide strip (if the dough sticks to the surface, use a small offset spatula and quickly run it underneath the strip to loosen it). Carefully transfer the strip to the tart pan and form it around the inside of the foil to create the star shape with the dough (if the dough breaks, just use your fingers and the support wall to form it back together). Once formed, press the bottom of the star shape to adhere firmly to the bottom crust (it will feel like playdough and can easily be molded).
Bake until the crust is set and turns a light golden brown, 20 to 25 minutes. Transfer to a wire rack to cool slightly, about 30 minutes. Carefully remove the foil and discard.
Meanwhile, for the lemon curd: Whisk the sugar, lemon juice, eggs, yolk and milk in a medium saucepan over medium-low heat until combined. Add the butter a few pieces at a time and whisk continuously until the mixture is thick and coats the back of a spoon, 8 to 10 minutes. Strain the curd through a sieve if any lumps form. Pour the curd into the center star of the tart.
For the blueberry filling: Mix the blueberries, preserves, sugar, flour, lemon zest and lemon juice in a medium bowl until well combined and the berries look glossy. Spoon the mixture around the perimeter of the star where there is no curd.
Bake until the curd is set, 20 to 25 minutes. Transfer to a wire rack to cool slightly, about 30 minutes. Refrigerate to cool completely, 4 hours and up to overnight. Serve cold.
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