1/2 vanilla bean, split lengthwise and seeds scraped out and reserved
4 large egg yolks
1/2 cup sugar
3 tablespoons cornstarch
1/2 teaspoon fine sea salt or table salt
1 cup heavy cream
1 cup quartered strawberries
1 cup halved blackberries
1 cup blueberries
How to Make It
Make dough: Combine flours, cinnamon, sugar, and salt in bowl of a standing mixer. Add butter. Using the paddle attachment, mix on low speed until butter is smaller than pea-size but not totally crumbly. Whisk egg yolk and cream in a small bowl and add to flour mixture. Blend until dough just comes together and is smooth. Do not overmix--otherwise it will be tough.
Form dough into a disk. Wrap in plastic wrap and chill until firm, at least 2 hours and up to 4 days.
Make pastry cream: Heat milk and cream in a medium saucepan over medium-low heat until it begins to simmer. Stir in vanilla bean and seeds and let sit off the heat, covered, 30 minutes to develop flavor.
Rewarm milk mixture over medium-high heat until almost simmering. Meanwhile, mix yolks and sugar in a medium bowl. Whisk in cornstarch and salt. Slowly whisk hot milk mixture into yolk mixture, 1/2 cup at a time. Pour mixture back into pan and cook, whisking constantly, until as thick as pudding, about 4 minutes. Pour pastry cream through a strainer into a clean bowl (discard vanilla pod).
Lay a piece of plastic wrap against surface of pastry cream to prevent a skin from forming. Chill until cold, at least 3 hours and up to 4 days.
Meanwhile, form and bake tart shells: Set 10 mini brioche molds (for larger tartlets) or 20 to 24 tartlet pans (for mini tartlets) on a work surface about 1 inch apart. Roll dough out on a lightly floured surface until about 1/2-in. thick. Roll dough onto rolling pin, and then unroll over pans (it may not totally cover all the pans). Press dough into each pan, letting edge of pan cut the dough to fit. Press dough flush against bottom and sides of pan. Use your thumb or side of finger to cut and trim dough flush with pan's edge. If you have any cracks or holes, patch with extra dough from the edges. Transfer filled pans to a rimmed baking sheet.
Preheat oven to 325°. Set another empty mold or pan on top of each dough-filled mold or pan to keep dough from puffing up. If you don't have more pans, cover dough in each pan with parchment, cutting to fit. Fill parchment with baking beans or pie weights.
Bake shells until edges are light golden brown, about 10 minutes. Carefully remove top pan (or parchment with beans). Return shells to oven and bake until centers of dough look dry and are starting to turn deep golden brown, 7 to 10 minutes more. Let cool completely before removing shells from pans.
To assemble: In a medium bowl or the bowl of a standing mixer, whisk heavy cream until stiff peaks form. Fold half the chilled pastry cream into the whipped cream (save remaining pastry cream for other uses). Spread or pipe pastry cream into tart shells and top with a mix of berries.