Blueberry and Vanilla Custard Tart

Preheat and Prep: Preheat oven to 350°F (175°C). Lightly butter a 9-inch tart pan with a removable bottom. (5 minutes)

Make the Crust: In a medium bowl, whisk together flour, sugar, cinnamon, cream of tartar, and salt. Stir in melted butter, egg yolk, and vanilla until combined. (10 minutes)

Press the Crust: Firmly press 2/3 of the mixture into the bottom of the prepared tart pan. Sprinkle the remaining 1/3 around the edges, then press firmly and evenly into the sides, creating a slightly raised edge. Prick the bottom of the crust lightly with a fork several times. (10 minutes)

Egg Wash: Mix egg white and water together until combined. Brush a light layer of egg white over the bottom of the crust. Place the tart pan onto a baking sheet. (3 minutes)

Bake the Crust: Bake in the preheated oven until the crust begins to brown, about 25 to 27 minutes. Remove from the oven and cool for 15 minutes. Leave the oven on. (42 minutes)

Make the Custard: While the crust is cooling, whisk together egg yolks, sugar, and salt until thick and light in color. Mix in vanilla extract. Gradually add heavy cream, mixing gently but thoroughly. Carefully pour custard into the cooled crust. (10 minutes)

Bake the Tart: Place tart back into the oven and bake until custard is just set and lightly browned, about 30 minutes. Remove from the oven and cool to room temperature, at least 1 hour. (90 minutes)

Make Blueberry Topping: Place blueberries and sugar in a medium saucepan over medium heat. Cook, stirring occasionally, until berries begin to burst and release their juices, about 15 minutes. (15 minutes)

Thicken the Topping: Combine lemon juice and cornstarch in a small bowl. Add cornstarch mixture to the blueberries, stirring constantly, and cook until thickened, 1 to 2 minutes. Remove from heat and allow to cool to room temperature. (17 minutes)

Assemble and Chill: When both the tart and the blueberries have cooled, carefully spoon blueberries over the top of the tart, and spread gently into an even layer. Place tart into the refrigerator and chill for at least 2 hours. (2 hours)

Serve: Remove sides of tart pan, slice, and serve. (5 minutes)