In a food processor, combine all-purpose flour, confectioners' sugar, and salt, pulsing until mixed. Add cold, cubed unsalted butter, blending until the mixture resembles coarse crumbs. In a small bowl, whisk egg yolk with a tablespoon of cold water, then mix this into the crumb mixture until it forms a dough. Shape it into a disc, wrap in plastic, and refrigerate for 1 hour.

Roll the chilled dough into an 11-inch circle on a lightly floured surface, then transfer it to a tart pan, gently pressing it into place. Trim any excess dough hanging over the edges and freeze the crust for 30 minutes. Preheat your oven to 375°F (190°C). Line the crust with foil and add pie weights, baking for 30 minutes. Remove the foil and weights, then bake for an additional 5 minutes until lightly golden. Let cool completely.

In a saucepan over medium heat, whisk together lemon juice, lemon zest, egg yolks, honey, and salt until thoroughly combined. Cook this mixture, stirring constantly, until it thickens and coats the back of a spoon, about 7-10 minutes. Remove from the heat and stir in cold, cubed unsalted butter until melted and smooth. Strain the curd through a fine sieve to remove any lumps. Pour the lemon curd into the cooled tart crust and bake at 350°F (175°C) for 10-12 minutes. Allow to cool.

In a blender, puree fresh blueberries until smooth, then strain through a fine mesh sieve to remove skins. In a saucepan, combine the blueberry puree with honey and cornstarch mixed with a tablespoon of water. Cook over medium heat, stirring frequently, until the mixture thickens, about 5 minutes. Remove from heat and stir in a splash of lemon juice for brightness, then let cool slightly.

Once both the lemon curd and blueberry layers have cooled, carefully spread the blueberry mixture over the top of the lemon curd in the tart. Ensure an even layer for a beautiful presentation. Refrigerate the assembled tart for at least 2 hours to allow it to set properly.