Combine sugar, butter, lemon juice and lemon zest in heavy medium saucepan. Stir over medium heat until sugar dissolves and butter melts.
Whisk eggs in medium bowl to blend. Gradually whisk in sugar mixture. Return mixture to saucepan. Stir over medium-low heat until mixture thickens, about 3 minutes; do not boil.
Pour into bowl. Cool slightly. Cover and refrigerate until well chilled. (Can be prepared 3 days ahead.).
Mix flour and salt in processor. Add butter and cut in, using on/off turns, until mixture resembles coarse meal. Add water and blend until dough begins to clump together. Gather dough into ball; flatten into disk. Wrap in plastic and refrigerate 30 minutes.
Roll out dough on lightly floured surface to 11-inch round. Transfer to 9-inch diameter tart pan with removable bottom. Trim edges. Pierce pastry all over with fork. Freeze 15 minutes.
Preheat oven to 400°F
Line pastry with foil. Fill with dried beans or pie weights. Bake until sides are set, about 20 minutes.
Remove foil and beans and bake until crust is golden brown, about 25 minutes. Transfer crust to rack and cooll completely. (Can be prepared 1 day ahead. Cover and refrigerate.).
Spread lemon filling in crust. Cover and refrigerate at least 30 minutes or up to 2 hours.
Spoon whipped cream into pastry bag fitted with star tip. Pipe whipped cream rosettes around top edge of tart.