Beat egg whites (at room temperature) until soft peaks form; gradually add salt and 1/4cup sugar, 1 tablespoon at a time, beating until stiff peaks form. Set aside.
Heat 4 cups milk in a large saucepan to simmering . Drop egg white islands by tablespoonfuls into simmering milk. Cook each island 2 minutes on each side or until slightly firm . Remove islands with a slotted spoon, and drain on paper towels. Refrigerate until ready to serve.
Add remaining milk to hot milk in saucepan; heat to simmering. Combine egg yolks and 3/4 cup sugar in a medium mixing bowl; beat until thick and lemon colored. Gradually stir one-fourth of hot milk into yolk mixture; add to remaining hot milk, stirring constantly. Cook, stirring constantly, over low heat 20 minutes or until thickened. Let mixture cool slightly, and stir in vanilla. Chill mixture thoroughly.
Sprinkle remaining 1 cup sugar evenly in a 10-inch cast iron skillet; place over medium heat. Cook, stirring constantly with a wooden spoon, until sugar melts and turns light brown. Remove from heat.
Hold 2 dinner forks back to back. Dip the forks into the syrup, and as the syrup runs off, pull the forks apart, allowing the threads to spin down on a sheet of waxed paper. Repeat procedure until desired number of threads are spun. (If the syrup hardens, reheat to the syrupy stage over medium heat.)
Spoon chilled custard into a serving bowl. Mound islands on top of custard; top with spun sugar. Serve immediately.