In a large mixing bowl, combine all-purpose flour, confectioners' sugar, and kosher salt. Cut in cold unsalted butter until the mixture resembles coarse crumbs. In a separate bowl, whisk an egg yolk with a tablespoon of cold water, then add it to the flour mixture. Mix until a smooth dough forms, wrap in plastic wrap, and refrigerate for at least 1 hour.

Preheat your oven to 350°F (175°C). Roll out the dough on a lightly floured surface into a circle to fit a 9-inch tart pan. Transfer the dough into the pan, pressing it into the corners. Use parchment paper and pie weights for blind baking, then bake for 10-12 minutes until set and lightly golden.

In a medium saucepan over medium-low heat, whisk together fresh lemon juice, lemon zest, eggs, honey, and a pinch of salt. Cook, stirring constantly until thickened and reaches 165°F (74°C). Remove from heat and stir in cold unsalted butter and heavy cream until fully incorporated. Pour into the pre-baked tart crust.

Bake the filled tart for an additional 10-12 minutes until the lemon curd is slightly jiggly in the center but firm around the edges. Remove and cool at room temperature.

Puree fresh or frozen blueberries until smooth. Strain through a fine mesh sieve into a saucepan to remove seeds. Mix in honey and cornstarch, and simmer over medium heat, stirring constantly until thickened, about 3-5 minutes.

Once the blueberry mixture has thickened, pour it over the cooled lemon curd layer. Spread it evenly with a spatula. Refrigerate for at least 2 hours.

Slice the Blueberry-Lemon Curd Tart and serve on plates. Garnish with fresh mint or a sprinkle of lemon zest if desired.