Pour the cornmeal and powdered sugar into a large zip-top bag or large container with a tight fitting lid. Shake until mixed.
In a medium saucepan over low heat, melt the butter and white chocolate, stirring constantly until completely melted. Remove from heat.
Immediately pour melted mixture over cereal and stir gently to coat.
Pour cereal into prepared bag or container. Shake until everything is coated. Spread onto baking sheet lined with foil or parchment and allow to cool. Discard excess powder. Store in an airtight container at room temperature up to one week.