Rinse raisins briefly with boiling water, drain, and place in a bowl. Drizzle with rum and let stand. Sift flour into a mixing bowl. Add salt, powdered sugar, vanilla, grated lemon rind, egg yolks, and milk. Stir. Batter will be quite liquid. Let stand for approx. 30 minutes. 
Beat egg whites, powdered sugar and a few drops of lemon juice until whites form peaks. Gently fold egg whites into batter. 
Heat butter in large skillet. Add batter and spread raisins on top. Cover. Brown one side and then turn. Tear pancake into pieces with two forks and continue frying until done. 
Serve sprinkled with powdered sugar.