Butter and line the base of a shallow 23cm/9in cake tin.
Melt the chocolate and butter together, either in a bowl over simmering water, or in a microwave, it is quite easy to use the microwave for this as the amount of butter will limit the chance of the chocolate burning.
(I place the butter and chocolate in a bowl and start on full for 30 seconds and continue with this until all the butter is melted and the chocolate is melting too, don't worry about the butter not being completely melted at this stage as you can take it out and mix, the heat of the butter will continue the melting of the chocolate, if needs be you can put the mixture back in the microwave for 10-20 seconds and just mix again.)
Once you have the chocolate mixture ready, set aside to cool.
Whisk the eggs until pale, then add the sugar and whisk until thick and glossy and well combined. Gently fold in the melted chocolate mixture, then sift in the flour and baking powder and gently stir until smooth. You can use a hand whisk for this, but be gentle as you don't want to knock the air out of the eggs.
Pour into the prepared cake tin and bake for 45-50 mins, or until firm to the touch, use a tooth pick to check if it is done in the centre, there should be a few moist crumbs sticking to it. (You want that sticky moist centre). The centre will firm up while it is cooling.
Cool the brownies in the tin for 1 hour, I know this will be difficult as the smell of the brownies cooking seems to get into every corner of the house, but honestly it will make all the difference to the finished product. (Honest)....
Cut into 16 squares, but really it is up to you the size of the pieces you want to serve.
And all that is left to say is ENJOY....
I need to give credit to Good Food Magazine book, 101 cakes and bakes where i first found this recipe, it is a very handy little book, I have baked a number of recipes for it and tweaked them as I have gone along.