Place the butter in a small pan and heat it over medium heat. The butter will melt, then foam, and finally turn golden brown with a nutty aroma. Remove from heat and allow it to cool slightly.

Add the brown sugar and granulated sugar to a large mixing bowl. Pour the browned butter over the sugar.

Using a handheld electric mixer, beat the mixture for 2–3 minutes until the sugars begin dissolving (it will still feel slightly grainy, which is perfectly fine).

Add the egg yolk and whisk again for about 2 minutes until the mixture looks glossy and slightly thickened.

Add the sourdough discard and mix with a balloon whisk until fully combined.

Avoid using an electric mixer here — overmixing can develop gluten and make the cookies cakey.

In a separate bowl, mix together: flour, cocoa powder, baking soda and salt.

Cover the dough and place it in the fridge for 4 hours.

This step is important — chilling allows the flour and cocoa to hydrate and prevents the cookies from spreading too much.

Preheat the oven to 180°C (350°F).

Line two large baking sheets with parchment paper.

Divide the dough into 8 equal portions and shape each into a ball.

Place them on the prepared baking sheets, leaving plenty of space between each cookie.

Bake the cookies for 12–14 minutes.

The cookies should have crisp edges and slightly soft, puffy centres.

As soon as the cookies come out of the oven, drop the tray from about 20 cm height onto your kitchen worktop. This helps create those beautiful crackly tops.

Leave the cookies on the tray for 10 minutes so they can firm up. Then transfer them onto a cooling rack.