Heat oven to 160C/320F. Line and grease a 33x23cm tray.
Melt butter and chocolate gently until smooth.
Remove from heat, stir in sugar and then flour.
Stir in eggs until mixture is smooth, add nuts/extras as desired.
Pour mix into tray and put in oven
This is where the experimentation comes in. It will probably take between 45 minutes and an hour to bake the brownies, but start checking after 35 minutes. The brownies should be crisp on top but still sticky and chewy inside. If they stick to the paper and fall apart, bake the next batch for longer (at a lower heat if necessary). If they end up hard all through, they were in the oven too long. Good luck!

This recipe works with gluten-free plain flour.