Set a rimmed baking sheet on oven rack in center of oven. Preheat oven to 350°F. Prepare a 9- or 10-inch tart pan by spraying lightly with non-stick spray.
In a medium sized bowl, mix together powdered sugar, flour, and salt. Add butter, and mix ingredients together until a dough forms. Pat dough evenly into bottom and sides of tart pan.
Bake crust for 15 to 20 minutes, or until firm. Meanwhile, prepare filling.
In a medium sized bowl (you can use the same bowl), lightly whisk eggs. Add the rest of the ingredients and whisk until smooth. Carefully pour the filling into baked crust. I leave the crust in the oven and pour the filling into it so I don’t have to transfer it.
Bake for 40 minutes at 350°F or until mostly set. Cool completely on wire rack, at least 30 minutes. Remove sides from pan.
Dust with powdered sugar and slice. Serve at room temperature or chilled. Refrigerate leftovers.
Notes
If desired, make the tart with all lemon or all lime juice.