Mix water, crushed pineapple, tapioca and 1 Tbsp. butter and cook over medium heat until thickened. Let cool.
Cut 1/2 lb. butter into flour with pastry cutter until size of pea. Add salt, sugar, baking powder, egg yolks and sour cream. Mix until sticky ball forms. Split in half with one ball a little larger than the other.
Pat larger half in 15 1/2 x 10 1/2 pan with sides (1 inch) ungreased pan. Spread pineapple mixture over dough layer. Roll second half of dough between 2 sheets of wax paper (cut the size of your pan). Remove top sheet of wax paper and lay dough on top of pineapple mixture and pinch sides. Sprinkle top with walnut and sugar mixture.