Preheat oven to 375. Grease and flour one 8"X12" pan.

In med. bowl cream butter/margarine w/ sugar until light. Beat in eggs and rt.beer extract.

Combine flour, baking powder, and salt. Add to egg mixture. Beat in rt.beer and mix umtil just combined.

Pour batter into prepared pan and bake at 375 for 30-35 min. Let cool, then frost

To make frosting: In med. bowl beat the 1/2 cup butter, conf. sugar, 1 tsp rootbeer extract and pinch of salt. Beat in 1-3 tblsp rootbeer soda to reach desired consistency. Spread on cooled cake.