Preheat the oven to 180°C/350°F/Gas mark 4.
Grease a 33 x 23 x 5cm/13 x 9 x 2in cake tin
with margarine.
Place all of the ingredients except for the
chocolate chips and the icing sugar in
a large mixing bowl.
Beat together, using a
wooden spoon, until smooth. Then stir in the
chocolate chips.
Spoon the mixture into the
prepared cake tin and level the top. Bake in the
oven for 30 to 40 minutes, until risen and springy to
the touch. Leave to cool in the tin.
Once cool,
dust with icing sugar. Cut into squares to
serve.