Wash sweet potatoes; pierce with a fork. Bake in a preheated 350º oven on a greased baking sheet for about 1-1/4 hours or until tender.
Meanwhile, in a heavy small skillet, cook and stir pecans, granulated sugar, and the 1 Tbsp. butter over medium heat for 6 to 8 minutes or until sugar melts and turns golden brown.
Immediately remove from heat; spread nut mixture onto a second greased baking sheet; separate into clusters. Cool completely.
Lightly grease a 2-qt. square or rectangular baking dish. Scoop sweet potato pulp into a large mixing bowl; discard peel. Beat with an electric mixer on medium speed until smooth. Stir in liqueur, the 2 Tbsp. butter, the brown sugar, spice and salt. Beat until fluffy. Spread in prepared baking dish.
Chop nut mixture into small pieces; sprinkle on sweet potatoes. Bake, uncovered, about 30 minutes or until heated through.