Heat milk and vanilla bean in pan over medium heat until almost boiling. Remove from heat. Remove vanilla bean halves; scrape seeds into milk. Stir, then let stand, covered, to infuse, 5 to 10 minutes.
Place pan over medium-low heat; add white chocolate; whisk until completely melted. Serve immediately in mugs.
This is a great favor. I made them for a baby shower favor 3 years ago. Going to make them again (by request)..