Place pecans on large glass plate and microwave (MW) at HIGH (100% power) for 8 minutes, stirring at 2-minute intervals. Set aside. In 8-cup measure, MW butter on HIGH for 1 minute. Stir in brown sugar and milk until blended. MW on HIGH for 7 minutes, stirring at 2 minute intervals. Beat with wooden spoon until stiff, about 5 minutes. Stir in vanilla and roasted pecans. Spread in a lightly buttered 8-in-square glass dish; chill until firm. Cut into squares.