Preheat oven to 180ºC
In large bowl, combine margarine, sugar, flour, cocoa, baking powder, eggs, milk, and 1.5 tsp vanilla. Mix well.
Spread in greased 13 inchx9 inch pan. Bake 40 minutes.
Just before brownies are done, in heavy saucepan, over low heat, melt chips with condensed milk, and remaining vanilla. Remove from heat. Immediately spread over hot brownies.
Cool. Chill, cut into bars. Store covered, at room temperature.