For crust: Blend flour, sugar, and salt in processor. Add butter and cut in using on/off turns until mixture resembles coarse meal. Whisk egg yolk and 1 tablespoon ice water in small bowl to blend; add to processor and process until moist clumps form, adding more ice water by teaspoonfuls if dough is dry. Gather dough into ball; flatten into disk. Roll out dough on floured surface to 13-inch round. Transfer dough to 9-inch-diameter tart pan with removable bottom. Trim overhang to 1/2 inch. Fold overhang in and press onto sides, forming double-thick sides. Pierce crust all over with fork. Freeze crust 30 minutes.
Preheat oven to 375°F Line crust with foil; fill with dried beans or pie weights. Bake until crust sides are light brown, about 25 minutes. Remove foil and beans; bake until crust is cooked through and golden brown, about 20 minutes longer. Cool crust completely in pan on rack.
For mousse: Combine white chocolate and 1/4 cup whipping cream in large metal bowl. Set bowl over saucepan of simmering water (do not allow bottom of bowl to touch water) and stir until chocolate is melted and smooth. Remove bowl from over water; cool chocolate mixture until lukewarm, about 15 minutes.
Beat remaining 1 cup whipping cream and vanilla in large bowl until peaks form. Using clean dry beaters, beat egg whites with cream of tartar in medium bowl until stiff but not dry. Fold whites into chocolate mixture, then fold in whipped cream. Transfer mixture to cooled crust; smooth top. Chill overnight.
Combine jam and lemon juice in small saucepan; bring to simmer, stirring over medium heat until jam melts. Remove from heat. Arrange sliced strawberries in concentric circles atop tart. Brush berries with melted jam mixture. Chill tart up to 2 hours and serve.