Instructions

for the tart crust

Whisk egg yolk, cream, and vanilla together in bowl. Grind Sucanat in spice grinder until fine and powdery, about 1 minute. Process flour, ground Sucanat, and salt in food processor until combined, about 5 seconds. Scatter chilled butter over top and pulse until mixture resembles coarse cornmeal, about 15 pulses. With processor running, add egg yolk mixture and process until dough just comes together, about 12 seconds.
Form dough into 6-inch disk, wrap tightly in plastic wrap, and refrigerate for 1 hour. (Dough can be wrapped tightly in plastic and refrigerated for up to 2 days or frozen for up to 1 month. If frozen, let dough thaw completely on counter before rolling.)
Let chilled dough sit on counter to soften slightly, about 10 minutes. Roll dough into 11-inch circle on lightly floured counter. Loosely roll dough around rolling pin and gently unroll it onto 9-inch tart pan with removable bottom, letting excess dough hang over edge. Ease dough into pan by gently lifting edge of dough with your hand while pressing into corners and fluted sides of pan with your other hand. Run rolling pin over top of pan to remove any excess dough. Wrap dough-lined pan loosely in plastic, place on large plate, and freeze until dough is chilled and firm, about 30 minutes. (Dough-lined tart pan can be wrapped tightly in plastic and refrigerated for up to 2 days or frozen for up to 1 month.)
Adjust oven rack to middle position and heat oven to 375 degrees. Set dough-lined tart pan on baking sheet, line with double layer of aluminum foil, covering edges to prevent burning, and fill with pie weights.
Bake until crust is golden brown and set, about 30 minutes, rotating pan halfway through baking. Remove weights and foil and let crust cool completely, about 1 hour.

for the filling

Meanwhile, decrease oven temperature to 350 degrees. Measure out and 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 food processor until smooth, about 2 minutes. Strain puree 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 remaining ⅛ teaspoon salt. Whisk cornstarch and water together in 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 platter or cutting board.