1. LINE a 33cm x 22cm pan with foil, letting some excess hang over the sides.
2. CREAM the butter and caster sugar until light and fluffy. Add the egg and vanilla, beat well and then stir in sifted flour and baking powder. Press mixture into pan and bake in a moderately hot oven 190°C for 25-30 minutes or until golden. Cool slightly in pan on a wire rack.
3. COMBINE the chocolate, butter and brown sugar in a saucepan and melt over a moderate heat, stirring often, until smooth. Remove from the heat and whisk in the extra eggs and vanilla. Whisk in the sifted extra flour and cocoa, and then stir in the pecans. Pour over the cooled base and bake for 25-30 minutes or until set.
4. COOL completely in the pan on a wire rack. Use the foil to lift from pan and then cut into 20 squares. Store in an airtight container until required.