Add the butter to a saucepan over medium heat. Use a pan with a light-coloured bottom so you can keep track of the colour progression.

Stirring often, allow the butter to melt completely.

Keep stirring. The butter will begin to foam, and the colour will progress from yellow to a golden-tan, and finally to a light brown.

When the butter is light brown in colour and has a nutty, caramelized aroma, immediately remove the pan from the heat.

Quickly transfer the butter (and its butter solid bits!) to a large heat-proof mixing bowl, and allow to cool slightly whilst you continue with the recipe.

Preheat the oven to 180C/350F/Gas 4, and line a baking tray with parchment paper, or a silicone mat. Set aside.

Whisk together the flour, baking powder, baking soda, cornflour, and salt. Set aside.

Once the brown butter has cooled slightly, add the milk and sugars, and whisk until combined. Add the egg and vanilla, and mix until combined.

Add the dry ingredients, and mix until just combined. Fold in the chocolate chips.

Roll the dough into 1.5oz balls, and place onto the prepared baking tray. Bake for 10 - 12 minutes.

Allow to cool on the baking tray for 5 - 10 minutes before transferring to a wire rack to cool completely.