In a large mixing bowl, combine all-purpose flour, confectioners' sugar, and kosher salt. Use a pastry cutter to cut in cold, unsalted butter until the mixture resembles coarse crumbs. In a separate bowl, whisk together the egg yolk, heavy cream, and vanilla, then add to the flour mixture. Combine until a dough forms, wrap it in plastic wrap, and chill it in the refrigerator for 1 hour.

Preheat your oven to 350°F (175°C) while you roll out the chilled dough on a lightly floured surface to about ¼ inch thick. Carefully fit the dough into a 9-inch tart pan, pressing it into the sides and removing any excess. Prick the bottom with a fork to prevent bubbling, then place it in the oven. Bake for 20-25 minutes, or until the crust is lightly golden and fragrant.

While the tart crust is cooling, prepare the lemon curd. In a medium saucepan, whisk together fresh lemon juice, lemon zest, eggs, and honey. Cook over medium-low heat, stirring constantly until the mixture thickens and reaches 165°F (74°C), about 10-12 minutes. Once thickened, remove from heat and stir in the unsalted butter until smooth and creamy. Pour the lemon curd into the cooled crust and spread evenly.

Return the tart to the oven and bake for an additional 10-12 minutes, or until the lemon curd is just set but still jiggles slightly in the center. Keep a close eye to avoid overbaking, as the curd will continue to firm up as it cools. Once done, allow the tart to cool completely at room temperature.

To make the blueberry filling, combine fresh or frozen blueberries in a saucepan over medium heat. Use a fork to mash the blueberries gently and cook for about 5 minutes, until they start to release their juices. Strain the mixture through a fine mesh sieve into a bowl, discarding solids, and return the liquid to the saucepan.

Add cornstarch and honey to the strained blueberry juice in the saucepan, and bring the mixture to a boil over medium heat while stirring continuously. Cook for 2-3 minutes, or until the filling thickens and becomes glossy. Remove from heat and allow it to cool slightly before proceeding to the next step to prevent mixing.

Once the blueberry filling has cooled slightly, gently pour it over the set lemon curd layer. Use a spatula to spread it evenly, creating a lovely visual layer atop the tart. Carefully refrigerate the assembled tart for at least 2 hours, allowing the flavors to meld and the layers to firm up beautifully.

After chilling, your Blueberry-Lemon Curd Tart is ready to serve! Slice it into wedges and garnish with fresh berries or mint leaves, if desired. The tart can be kept in the refrigerator for up to 3 days.