Combine flour, powdered sugar, vanilla, butter & salt together and mix until you have a nice dough. Mixture should hold together and not be too stiff or sticky. Press into 11x14 pan and bake for 15 minutes at 350 degrees F. Crust should be golden brown.
For top portion combine the 2 eggs, sugar, Tang powder and lemon juice in a bowl. Mix until well blended, but do not whip. Pour mixture on top of crust. Bake for 20 minutes, or until top portion is firm, at 350 degrees. Let cool and then dust with powdered sugar.