Cook and drain macaroni as directed on package.
Move oven rack to lower third of oven. Heat oven to 350 degrees F. Lightly grease 12 regular-size muffin cups.
In medium bowl, mix crushed cereal, 1 cup of the cheese and 4 tablespoons of the melted butter. Divide mixture among muffin cups; press firmly in bottom and up sides of cups with spoon.
In 3-quart saucepan, stir together remaining 1 tablespoon melted butter and flour with whisk; cook over medium heat 1 minute. Gradually stir in warmed milk with whisk; cook and stir about 5 minutes or until thickened. Remove from heat; stir in 1 cup of the cheese until melted. Stir in cooked macaroni, egg yolk and salt. Fold in beaten egg white. Spoon about 1/4 cup mixture into each crust-lined cup. Top with remaining 1/2 cup cheese.
Bake about 20 minutes or until golden and puffed. Cool 5 minutes; remove from pan. Serve warm.