1. Heat oven to 160 degC fan bake. Line a 17cm x 27cm slice tin with nonstick baking paper.
2. Place coarsely chopped butter and chocolate in a heatproof bowl over a saucepan of simmering water, or microwave for 2 to 3 minutes, to melt. Whisk until smooth, then stir in sugar and lightly beaten eggs.
3. Sift plain flour and cocoa powder together, then stir into chocolate mixture. Lastly, gently stir in chocolate chips.
4. Pour into prepared tin. Bake for 1 hour or until an inserted skewer comes out moist but clean. Cool, then remove from tin and cut into slices. Dust with icing sugar before serving.

Tip: If you want to add something extra to this mixture, stir half a cup of toasted nuts - such as peanuts, almonds or walnuts - into the mixture before baking or replace the chocolate chips with white chocolate bits for a change.