PREHEAT oven to 375°F. Line a 9- x 9- x 2-inch baking pan with Reynolds Parchment Paper; set aside.
FOR CRUST: Combine flour, powdered sugar and butter until crumbly; press into parchment-lined pan.
BAKE 15 minutes; remove from oven.
FOR LIME FILLING: While crust is baking, combine sugar, lime juice, 6 egg yolks and butter in a medium saucepan. Cook over medium heat, whisking frequently until thickened, about 8 to 10 minutes; set aside.
FOR MERINGUE: Combine 3 reserved egg whites and cream of tartar in a medium bowl (reserve remaining egg whites for another use or discard). Beat on high speed with an electric mixer until soft peaks form. Continue beating about 2 minutes, gradually adding sugar until stiff peaks form; set aside.
SPREAD lime filling evenly over warm crust. Spread meringue evenly over lime filling. Sprinkle coconut over meringue. Return to oven.
BAKE 10 to 13 minutes or until coconut is lightly browned. Remove from oven, cool completely. Use edges of parchment lining to lift dessert from pan. Place on cutting board. Pull back edges of parchment for easy cutting. Cut into 16 squares. Serve immediately or refrigerate.