This traditional egg custard-filled French dessert, from pastry chef Sebastien Rouxel of Bouchon Bakery, requires only simple ingredients and makes for a delightful ending to an Easter menu.
Pate Brisee: Place the flour and salt in the bowl of an electric mixer fitted with the paddle attachment; with the mixer on low, add butter. Increase speed to medium and mix until butter is well combined. Slowly add water and mix until fully incorporated.
Turn dough out onto work surface and flatten into a disk. Wrap with plastic wrap and refrigerate for at least 1 hour.
Line a baking sheet with a nonstick baking mat or parchment paper. Place a 9-by-2-inch baking ring on prepared baking sheet and brush sides with canola oil; set aside.
Roll out dough on a lightly floured work surface until it is 3/16-inch thick and 14 inches in diameter. Gently fit dough into prepared baking ring, leaving an overhang of about 2 inches, reserving any scraps. Transfer baking sheet to refrigerator or freezer and chill for 20 minutes.
Preheat oven to 350 degrees.
Line dough with parchment paper and fill with pie weights. Transfer to oven and bake until edges of dough are lightly browned and bottom is set but still light in color, about 45 minutes.
Carefully remove parchment paper and pie weights. If any holes or cracks have appeared in the dough, patch with reserved dough scraps. Brush with egg and return baking sheet to oven. Bake until bottom is golden brown, about 25 minutes. Transfer baking sheet to a wire rack; let tart shell cool completely.
Filling: Preheat oven to 350.
Place eggs yolks, eggs, sugar, and vanilla bean seeds in a large bowl; whisk to combine. Add custard powder and cornstarch; whisk for 30 seconds to incorporate. Slowly add milk, whisking to combine. Strain into a large saucepan.
Place saucepan over medium-high heat. Bring mixture to a boil, whisking gently to avoid forming air bubbles; Let boil for 1 minute, whisking gently but constantly to avoid scorching. Transfer custard to the bowl of an electric mixer fitted with the paddle attachment; mix on low to cool and slightly emulsify custard.
Meanwhile, arrange prunes in tart shell; pour custard over fruit, keeping in mind you may not be able to fit all of the custard. Transfer to oven and bake until set but with a slight jiggle and a dark brown skin has formed on top, about 1 hour and 20 minutes to 1 hour and 40 minutes. Remove from oven and let cool to room temperature.
Transfer tart to refrigerate and chill for 12 hours. Using a serrated knife, trim away excess crust from top edge of baking ring. Tilt ring on its side with the bottom facing you and run a small paring knife between the crust and the ring to release the tart. Set tart down and carefully lift ring to remove. Refrigerate tart until ready to serve, up to 2 days.