Preheat the oven to 180C or 356F. Place a tiny bit of butter or oil on 2 baking sheets and then line with baking paper. The butter will stop the baking paper moving around as you spoon the mixture on – it’s quite stiff.
Brown the butter in a small saucepan over a low-medium heat. It should weigh just under 25g once browned. Pour the butter into the bowl of your kitchen mixer, using a silicon spatula to get every last skerrick from the saucepan.
1/4 fill the saucepan with water and place it back on the heat. Atop the saucepan place a heatproof bowl and add the chocolate. Make sure the water doesn’t touch the bottom of the bowl or you burn the chocolate, which would be tragic. As soon as it has fully melted, take it off the heat, wipe the water off the bottom of the bowl and set aside.
Add the caster sugar to the butter and mix until just combined – it will look like damp sand. I like to use my balloon whisk attachment for this.
Crack the eggs into a bowl (I have been burned by a bad egg in cookie dough before) and add them to the stand mixer. Turn the speed up to high (around a 6 on a KitchenAid) and beat for 7-10 minutes, until the mixture is light and fluffy.
Once the egg mixture is ready, stop the mixer and add in the melted chocolate. Use the silicon spatula to get it all out. Whisk on low for a minute or two until combined, scrape down the bowl, and then add the remaining ingredients – cocoa, baking powder, salt, and vanilla bean paste, if you’re using it. Return the mixer to a low speed and mix until combined, scraping down the sides if necessary.
Use two spoons to form 8-10 circular cookies evenly across the two baking sheets. They don’t spread much, but leave room between each cookie.
Try to make the tops as smooth as possible, but know that you can allow them to harden a bit before smoothing them out with your hands, very lightly moistened with water if necessary.
Place each sheet of cookies in the oven for 10-12 minutes. They will look done by 8 minutes, but will still be very malleable underneath. For best results, allow the cookies to cool completely before removing them from the baking tray. They keep well for a few days in an airtight container – I like to keep mine in the fridge so they’re nice and chewy.
If you’re a sea salt fiend, they are delightful with a small sprinkle of Maldon on top.