How to Make It
In a food processor, combine the flour, sugar, baking powder, lemon zest and salt. Add the butter in clumps and pulse until the mixture resembles coarse meal. Add the whole eggs and egg yolks and pulse a few times, until the dough just comes together. Turn the pastry dough out onto a lightly floured work surface and knead it 2 or 3 times, just until it comes together. Divide the pastry dough into 2 pieces, 1 slightly smaller than the other. Pat the pastry dough into disks, wrap each disk in plastic and refrigerate for at least 30 minutes.
In a medium saucepan, heat the milk with 1/4 cup of the sugar, the vanilla bean and vanilla seeds and the lemon zest until the mixture is hot to the touch. In another medium bowl, whisk the egg yolks with the remaining 1/4 cup of sugar until blended. Stir in the flour until incorporated. Whisk in the hot milk in a thin stream.
Set a fine-mesh strainer over a medium bowl. Pour the pastry cream mixture back into the saucepan and cook over moderate heat, whisking, until thick and bubbling, about 2 minutes. Immediately strain the pastry cream into the bowl, scraping the strainer with a rubber spatula. Press a sheet of plastic wrap directly onto the surface of the pastry cream and refrigerate until chilled, 1 to 2 hours.
Preheat the oven to 350°. Butter and flour a 10-inch fluted tart pan with a removable bottom. On a lightly floured work surface, roll out the larger disk of pastry to an 1/8-inch-thick round. Ease the pastry into the tart pan, pressing the dough into the corners. Don't trim the overhang.
Spread the chilled pastry cream in the tart shell in an even layer. Roll out the remaining pastry disk to an 1/8-inch-thick round and set it over the tart; gently press out any air bubbles. Carefully roll the rolling pin over the tart pan rim to cut off the overhanging dough. Gently press the edge together to seal the tart.
Bake the tart in the lower third of the oven for about 40 minutes, rotating the tart pans halfway through baking, until the crust is golden brown. Let the tart cool completely in the tart pan. Unmold the tart and transfer it to a large serving plate. Sprinkle the tart with pine nuts, cut into wedges and serve with berries.