2 (14 ounce) cans sweetened condensed milk
1 1/4 cups spiced rum
Remove the labels from the cans of milk. Place the cans into a large saucepan, and cover with a few inches of water. Bring to a boil over high heat, then reduce heat to medium, cover, and simmer for 4 hours. Keep an eye on the water level, and add water as needed to keep at least an inch of water above the cans. After the cans have boiled for 4 hours, remove from the boiling water and set aside to cool for 35 minutes.
Open the cans and scrape the browned milk into a bowl, whisk in the spiced rum until smooth, then pour into a bottle with a top. The liqueur will keep for several months in the refrigerator.