Instructions

1. In a food processor pulse together all the flour, cornmeal, 1½ tbsp (22 ml) sugar, thyme, salt and lemon zest until combined. Add 6 tbsp (90 ml) butter and pulse until mixture resembles coarse meal. Whisk together 2 egg yolks and 2 tbsp (30 ml) cold water in small bowl. With machine running, add to flour mixture through feed tube, mixing only long as it takes for dough to hold together.
2. Turn out dough onto clean work surface. Form into disk, wrap in plastic wrap and refrigerate for 1 hour.
3. On lightly floured work surface, roll dough out into a 10-in (25 cm) round before transferring to a 9-in (23 cm) tart pan with removable bottom. Press into corners and trim edges flush with rim of pan. Freeze until firm, about 30 minutes.
4. Meanwhile preheat oven to 375 F (190 C). Prick bottom of tart shell all over with fork before lining with aluminum foil and filling with dried beans or rice. Bake until edges start to brown and look dry, about 15 minutes. Remove foil and beans and continue to bake crust until golden brown and crisp, another 10 to 12 minutes. Let cool completely on wire rack.
5. To make filling, sprinkle gelatin over remaining 1 tbsp (15 ml) cold water in small bowl, and let stand until softened, about 5 minutes.
6. Whisk together remaining 6 egg yolks, 1 cup (250 ml) sugar, and salt in large heatproof bowl. Gradually whisk in lemon juice. Place bowl over saucepan of simmering water and whisk constantly until mixture has thickened and registers 160 F (70 C) on an instant-read thermometer. Remove from heat and whisk in gelatin mixture. Whisk in remaining ½ cup (125 ml) butter, a few pieces at a time, until smooth and well incorporated. Let cool to room temperature, stirring occasionally. Spoon filling into cooled crust and let set for 5 minutes. Dollop crème fraîche over filling and using a wooden skewer or tip of a knife, swirl into filling to create a marbleized effect. Refrigerate until filling is set, about 2 to 4 hours.