Heat the butter for a few minutes to melt down until smooth
Once melted, keep cooking the butter in the pan for a further few minutes, for the milk solids to start to brown. You are looking for a deeper caramel colour
Make sure to swirl the pan and stir slightly to stop anything from burning
Once browned, pour the brown butter into a new bowl to cool
Preheat the oven to 180ºc/160ºc fan and line a 9” square tin with parchment paper
Add the browned butter to a mixing bowl, with the sugar, and beat together until combined
Add the egg, and vanilla and mix again
Add the flour, cornflour, bicarb and salt and combine
Add the chocolate and mix through (you can use as much or as little as you want between 100-300g - I tend to use all 300g as I like it chocolatey)
Press into the base of the tin and bake for 20-22 minutes
Leave to cool for at least 30 minutes in the tin and enjoy
Notes
It’s best to use a block unsalted butter when making browned butter - using a margarine won’t work in the same way as it’s not butter.
If you want to add cocoa powder to make them chocolate flavoured, you can remove the cornflour, and 25g of plain flour, and add in 35g cocoa powder total - generally you need slightly less dry ingredients for a chocolate base as cocoa is more drying.
These will last 5-7+ days at room temperature, or in the fridge