Brown your butter. This involves melting the butter in a saucepan over a medium heat until brown flecks appear. Make sure to check out my post on how to brown butter if you're unsure. Leave cool in another bowl.
Prepare a 9 x 9 inch tray and preheat your oven to 180°C/fan 170°C.
In your mixing bowl, beat your sugar, eggs and vanilla. If you have a free standing mix, then turn the speed to low and stream in your cooled brown butter. If, like me, you have a handheld whisk, then add the butter gradually. Continue mixing until all combined.
Add in your flour and salt and mix through. Finally fold through whatever additions you fancy - chocolate, nuts, sprinkles.
Once your chocolate is evenly mixed through, pour your mixture into your prepared tin and smooth the surface. Bake for 30-35 minutes, or until the edges are set but the centre still looks a little gooey.
Allow to cool almost completely before cutting into them. I'm excited for you!