Place flour on pastry board and make a well in the center. Add salt and work quickly to a paste with the ice water. Roll out to about 20 × 20 inches if your board is large enough. Place the butter in the center of the dough. Fold it like an envelope and put it in the refrigerator for 20 minutes.
Remove and roll into a long strip. Fold in thirds with open ends out. Roll again. Fold again, envelope fashion, wrap in a small towel and return to the refrigerator for ½ hour. Repeat this process 3 times. The last time roll vary thin and cut into 3 long strips about 3 inches wide. Place on cookie sheets which have been moistened with water. Put the sheets in the refrigerator for 15 minutes.
Bake 15 minutes in a preheated 400° oven. Let cool, then spread with cream filling. While still warm, cut into triangles.
Put eggs, egg yolks, flour and sugar in a mixing bowl. Beat well. Blend in the cornstarch and vanilla, mixing well. Pour the hot milk over it.
Place over a moderate heat until it comes just to the boiling point. Remove from heat and place over a pan of ice. Stir until it begins to thicken.
Beat egg whites until stiff. Whip cream. Fold alternately into cooked mixture. Fold in rum. Spread filling over strips, and dust with powdered sugar.