Whisk together sugar, flour, eggs, and milk in a heavy saucepan. Cook over medium heat, whisking constantly, 10 minutes or until a chilled pudding-like thickness. Remove from heat; stir in 1 cup sweetened coconut and vanilla. Cover and chill 6 to 24 hours. Bake frozen tart shells according to package directions, and cool completely. Spoon custard into tart shells. Dollop with sweetened whipped cream; sprinkle with additional coconut.