¼ cup lemon zest plus ½ cup juice (4 lemons)
1 large egg plus 5 large yolks
⅓ cup plus ¼ cup honey
4 tablespoons unsalted butter, cut into 4 pieces and chilled
2 tablespoons heavy cream
1 recipe Classic Tart Crust (see below) partially baked and cooled
10 ounces (2 cups) blueberries
2 tablespoons cornstarch
2 tablespoons water
Adjust oven rack to middle position and heat oven to 350 degrees. Measure out 1 tablespoon lemon juice and set aside. Whisk remaining lemon juice, lemon zest, egg and yolks, ⅓ cup honey, and pinch salt in medium saucepan until smooth. Cook over medium-low heat, stirring constantly with rubber spatula, until mixture thickens slightly and registers 165 degrees, about 5 minutes.
Off heat, whisk in chilled butter until melted. Strain lemon curd through fine-mesh strainer into bowl, then gently stir in cream with rubber spatula.
Pour warm lemon curd into cooled tart crust. Set tart on baking sheet and bake until filling is shiny and opaque and center jiggles slightly when shaken, 10 to 12 minutes, rotating pan halfway through baking. Transfer tart with baking sheet to wire rack and let cool slightly.
Meanwhile, process blueberries in a food processor until smooth, about 2 minutes. Strain purée through clean fine-mesh strainer into medium saucepan, pressing on solids to extract as much liquid as possible (you should have about ¾ cup); discard solids.
Whisk in remaining ¼ cup honey and ⅛ teaspoon salt. Whisk cornstarch and water together in a small bowl, then whisk into strained blueberry mixture. Bring to simmer over medium-low heat, stirring constantly, and cook until thickened slightly and registers 170 degrees, about 4 minutes.
Off heat, whisk in reserved 1 tablespoon lemon juice. Pour blueberry mixture evenly over cooled lemon filling. Tap pan lightly on counter to release any air bubbles, then refrigerate until blueberry mixture is set and shiny, about 2 hours. To serve, remove outer ring of tart pan, slide thin metal spatula between tart and tart pan bottom, and carefully slide tart onto serving patter or cutting board.