Butter a 9-inch or 10-inch springform cake pan. Set aside 3/4 cup of the crumb dough to sprinkle over the top. Press crumb mixture on bottom and up sides of form (as much as will stick).
Preheat oven to 325 degrees. Mix butter, egg yolks, sugar together. Add cheese, vanilla, grated rind and lemon juice, flour and baking powder. Beat 4 egg whites until peaked. Fold into cheese mixture and pour on top of dough. Add chopped walnuts to reserved crumb mixture and sprinkle mixture over the top.
Bake for 1 hour or until set. Turn off heat, open oven door and let stand for 1 hour or until cooled. Remove rim of spring form pan and set cake with its cake bottom on serving plate.