Line a 9-in. square pan with foil; grease foil with 1 teaspoon butter. In a large heavy saucepan, cook and stir white chocolate over low heat until melted. Add milk and remaining butter; stir until blended. Remove from heat; stir in pecans and Kahlua., Spread into prepared pan. Refrigerate, covered, 2 hours or until firm. Remove foil; cut fudge into 1-in. squares. Store between layers of waxed paper in an airtight container in the refrigerator.