Beat the butter in large bowl on medium speed until smooth and creamy, about 2 minutes. Beat in brown sugar until fluffy, about 2 minutes. Beat in eggs, one at a time; scrape down the side of the bowl frequently to keep the batter smooth. On low speed, beat in the flour mixture in 3 additions alternately with the bourbon mixture. Stir in the pecan pieces until evenly distributed. Pour into the prepared tube pan. Arrange the pecan halves in concentric circles over the top of the cake. Cover the pan loosely with aluminum foil.