First make the brown butter: pop the diced butter into a medium-sized non-stick saucepan and set over medium heat. Stir gently until completely melted. Increase the heat to medium and allow the butter to bubble, stirring often. It will bubble and spit – don’t panic, this is normal (just take care!).
Continue to cook the butter, stirring to ensure it cooks evenly, until the crackling noises fade and the bubbles subside. At this point, you should see a foam appear on the surface and the colour will change from golden-yellow to light brown to deep amber brown. This can take anywhere between 7-10 minutes, depending on the size of your pan and how high your heat is. Watch the pan closely as it takes just seconds to go from brown to burnt.
As soon as brown flecks start to appear and you start to smell a gorgeous nutty aroma, remove from the heat. Quickly, but carefully, pour into a medium-sized heatproof bowl. This stops it cooking any further. Leave to cool slightly. It doesn’t need to be room temperature but shouldn’t be scorching hot. You can make the brown butter up to 2 weeks in advance and keep it chilled in your fridge. Allow to come to a softened room temperature before making the cookies.
In a large mixing bowl, add the brown butter, caster sugar and soft light brown sugar. Using an electric whisk, beat together. You can use a wooden spoon too.
Add the egg and vanilla extract and mix again until combined.
Add the plain flour, bicarbonate of soda and salt. Mix until you have a smooth dough.
Cover and chill in the fridge for at least 30 minutes - ideally overnight. I know it is tricky, but I promise it does make a difference and will be worth the wait! You can freeze at this point too.
When you are ready to bake the cookies, preheat the oven to 190°C/170°C Fan. Line a couple of baking sheets with non-stick baking paper and set aside.
Use an ice cream scoop or a spoon to scoop the dough into about 10-12 balls. Place on lined baking sheets as they do spread so I found doing 4 on a sheet worked best.
Bake for 8-10 minutes until just set. The edges will just be set and the middle will still look very soft - they harden as they cool, so don’t overcook them. Sprinkle with flakey salt whilst hot.
As soon as the cookies come out of the oven, take a large cookie cutter or a glass and gently swirl it around each cookie to create the perfect circle shape. - whatever you’re using must be larger than the cookie or you get weird edges but this gives the cookies a lovely shape.
The video below will help with this recipe.