Remove center from top of cake, leaving a shell at least 3/4 inch thick.
Fill with ice cream and sprinkle 1/2 cup sliced nuts over ice cream.
Beat egg whites until stiff but not dry; beat in salt, sugar and vanilla gradually.
Spread on top of cake and sprinkle with remaining Brazil nuts.
Bake in very hot oven (450°F.) until light brown, about 5 minutes.
Serve at once.