Actress Rashida Jones joins Martha to make a rhubarb tart. Part 1.
Make the cornmeal crust: Process flour, cornmeal, granulated sugar, lemon zest, and salt in a food processor until combined. Add butter, and process until mixture resembles coarse crumbs, about 20 seconds. Beat yolks and water in a small bowl. With machine running, pour yolk mixture into flour mixture; process until just combined, about 20 seconds. Shape dough into a disk; wrap in plastic. Refrigerate for at least 1 hour or up to 2 days.
Preheat oven to 375 degrees. Roll dough on lightly floured parchment to 1/4-inch thickness. Fit into a 10-inch springform pan. Refrigerate until dough is cold and firm, about 20 minutes. Line dough with parchment, and fill with pie weights or dried beans. Bake until edges begin to turn gold, about 25 minutes. Carefully remove weights and parchment. Reduce oven temperature to 350 degrees, and bake until golden brown, 20 to 25 minutes. Let cornmeal crust cool in pan on a wire rack.
Make the lemon-yogurt mousse: Sprinkle gelatin over cold water in a small bowl, and let stand until softened, about 5 minutes. Combine 1 tablespoon cream and the brown sugar in a small saucepan over medium heat, stirring until sugar dissolves and mixture is warm. Stir in gelatin mixture, and remove from heat. Combine yogurt, lemon zest, and salt in a medium bowl. Add brown-sugar mixture, and whisk until smooth. Whisk remaining 3/4 cup cream in a medium bowl until peaks form. Gently fold cream into yogurt mixture.
Pour lemon-yogurt mousse into cornmeal crust. Cover, and refrigerate until firm, at least 4 hours or overnight.
Make the rhubarb topping: Bring granulated sugar and water to a boil in a medium saucepan, stirring until sugar dissolves. Cook, undisturbed, until light amber, about 7 minutes. Remove from heat; add 3/4 cup brandy, the cinnamon stick, peppercorns, vanilla, and salt. Return mixture to a boil for 1 minute, then stir in rhubarb. Remove pan from heat, cover, and let stand for 5 minutes. Stir in lemon juice and remaining 1/4 cup brandy, re-cover, and let stand for 20 minutes more. Refrigerate until cold, about 4 hours. Strain, reserving liquid, and discard cinnamon and peppercorns. Boil reserved liquid in a medium pot until reduced to 1 1/2 cups, about 4 minutes. Let cool.
Spoon the strained rhubarb over the mousse, and serve immediately with the rhubarb reduction on the side.