Preheat your oven to 350°F (175°C). In a food processor, combine all-purpose flour, confectioners' sugar, and kosher salt, pulsing until mixed. Cut in chilled unsalted butter until the mixture resembles coarse cornmeal. Add an egg yolk and blend just until a dough forms. Shape the dough into a disk, wrap it in plastic, and refrigerate for at least an hour to firm up.

Flour a clean surface and roll the dough into an 11-inch circle, about 1/8 inch thick. Transfer the rolled dough to a 9-inch tart pan, gently pressing it into the bottom and up the sides. Trim any excess dough, then place the crust in the refrigerator for another 15 minutes to chill before baking.

In a saucepan, whisk together lemon juice, lemon zest, eggs, honey, and a pinch of salt. Over medium heat, stir continuously until the mixture thickens and reaches 165°F (74°C); about 8–10 minutes. Remove from heat, strain through a fine sieve, and whisk in chilled butter until fully melted. Pour the lemon curd into the prepared crust.

Place the tart in the preheated oven and bake for 10–12 minutes, until the filling appears shiny. Allow it to cool for 15 minutes at room temperature before transferring to the refrigerator to chill completely.

Blend fresh blueberries in a blender until smooth. Strain the mixture through a fine sieve. In a saucepan over medium heat, whisk the blueberry puree with honey and cornstarch. Cook until thickened and reaches 170°F (77°C), about 5–7 minutes. Set aside to cool slightly.

Pour the blueberry mixture over the cooled lemon curd layer. Tap gently on the counter to release air bubbles. Cover with plastic wrap and refrigerate for at least 2 hours until set.

Slice the Blueberry-Lemon Curd Tart and serve cold. Optionally top with whipped cream or vanilla ice cream.