Special equipment: a 9-inch tart pan with 1-inch sides; 2 piping bags fitted with different-sized star tips
For the shortbread crust: Position an oven rack in the bottom third of the oven and preheat to 350 degrees F. Spray a 9-inch tart pan with cooking spray.
Add the flour, butter and confectioners' sugar to a food processor and pulse until the mixture resembles coarse meal with some pea-size pieces. Add the egg and pulse until the dough comes together.
Press the dough into the bottom and up the sides of the prepared tart pan. Prick the dough all over with a fork. Bake until the crust is golden brown, 20 to 25 minutes. Let cool slightly on a rack while you make the filling.
For the lemon curd: Meanwhile, whisk the lemon juice, granulated sugar, milk, whole eggs and yolks in a medium saucepan over medium heat until well combined. Add the butter and cook, stirring continuously, until the mixture thickens and coats the back of a spoon, 10 to 12 minutes. Strain the curd if any lumps form; set aside.
For the strawberry puree. Blend the strawberries in a blender until fully pureed. Strain the puree through a fine-mesh strainer into a small saucepan to remove the seeds. Add the granulated sugar and lemon juice, bring to simmer and simmer, stirring often, until the puree is syrupy and yields about 1/4 cup, about 15 minutes. Let cool slightly.
Add the strawberry puree to the lemon curd and mix until fully combined. Pour into the cooled crust and smooth with a spatula. Bake until the curd is set, 15 to 20 minutes. Let cool slightly on a rack, about 30 minutes, then refrigerate, uncovered, until completely cool, about 2 hours.
For the meringue: Fit a metal bowl over a pot with about an inch of simmering water (make sure the bowl does not touch the water). Put the granulated sugar, cream of tartar and egg whites into the bowl and hand whisk until the sugar is fully dissolved and the whites are warm to the touch, 3 to 3 1/2 minutes. Test the mixture by rubbing it between your fingers to make sure it's not grainy. Transfer to a stand mixer with a whisk attachment, add the vanilla extract and whip, starting on a low speed and gradually increasing to high, until the mixture forms stiff, glossy peaks, about 4 minutes. Transfer the meringue to 2 piping bags fitted with different-size star tips. Pipe the meringue in a decorative pattern on top of the tart, leaving some of the pink filling showing.
To serve: position an oven rack in the top position and preheat the oven to broil. Broil the tart until the meringue is toasted, 30 seconds to 1 minute. Garnish with curled strips of lemon zest.
When measuring flour, we spoon it into a dry measuring cup and level off the excess. (Scooping directly from the bag compacts the flour, resulting in dry baked goods.)
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