In a large container combine whiskey, lemon, sugar, milk, chocolate squares and vanilla beans. Keep at room temperature for 10 days, stirring once a day.
After 10 days, remove the lemon half, chocolate and vanilla beans. Insert a coffee filter or muslin into a large funnel. Pour the liquid through the filter into a large pitcher or jug. Change filter as needed. A clear yellow solution should result. This liqueur can be stored in a sealed bottle at room temperature.