Place the sweet potatoes into a large pot and cover with salted water. Bring to a boil over high heat, then reduce heat to medium-low, cover, and simmer until tender, about 20 minutes. Drain and allow to steam dry for a minute or two.
Return the pot to the stove over medium heat. Add the butter and brown sugar; cook and stir about 5 minutes until the sugar begins to caramelize. The sugar will be foamy at first, then the foam will subside and the sugar will begin to caramelize; cook until the color darkens slightly. Carefully stir in the coffee liqueur, then return the potatoes to the pot. Stir in the raisins and toasted pecans until the potatoes are slightly mashed and everything is well mixed.