Crush the rusks/toast until they are fine crumbs. (If you can't find holland rusks, I found 2-3 packages of mini-toasts from Trader Joes, or Zweiback toask, seems to do just as well.) Melt the butter. Add the sugar and mix. Add the crushed rusks in. After everything is mixed, line a 13" x 9" pan with 3/4 of the mixture, saving the rest to sprinkle on the top. Do not press the mixture down, just pat it into place.
Beat egg whites until stiff. Add sugar and beat until spreadable.
Mix constarch and sugar. After they are well mixed, add in the remaining ingredients. Cook over medium heat, stirring constantly until it is thick. Pour custard into the pan. Spread the meringue on top of the custard. Sprinkle remaining crumb mixture on top. Bake at 300oF for 25 minutes or until the meringue is brown.