Peel and thinly slice 2-3 bananas. Set aside.
Combine 1/2 cup sugar, cornstarch, egg yolks, and salt in a large bowl. Whisk until smooth.
In a medium saucepan, heat 3 cups milk to a simmer. Gently whisk 1 cup hot milk into the egg mixture to temper it. Return mixture to saucepan with remaining milk.
Cook over medium heat, stirring constantly, until pudding thickens and bubbles gently (about 8-10 minutes). Remove from heat and stir in butter, vanilla, and remaining sugar (1/2 cup). Churn in a blender or whisk thoroughly until smooth.
In a 9″x13″ dish, arrange a layer of cereal, then banana slices, then half the pudding. Repeat layers. Finish with a top layer of cereal and a drizzle of pudding. Chill for 4 hours to set and develop flavors.