Preheat the oven to 160°C fan. Butter and line the springform pans. I used a 7-inch and 10-inch springform pan.

In a pot over medium heat, pour the Guinness beer and add the butter. Stir until the butter has melted, then turn off the heat.

Whisk in the brown sugar, caster sugar, cocoa powder and coffee powder.

In a separate bowl, whisk the eggs, yoghurt and vanilla extract. Whisk into the Guinness mix.

Sieve the flour, baking soda and salt into the mix and fold.

Pour the batter into the springform pans and bake for 45 mins. Check for doneness, and add time as needed.

In the meantime, to make the icing, add butter to a saucepan over medium heat. Stir constantly until deep golden brown.

Pour the butter, along with the brown whey solids into a bowl and let it cool, before refrigerating to solidify.

In the same saucepan, add the Guinness beer and reduce over medium heat to a thick syrup. It should taste very bitter but not burnt. Leave to cool.

In a large mixing bowl, add the solidified brown butter and the Guinness syrup, and whisk until creamy.

Fold the icing sugar in small batches with a spatula. Once all the sugar is incorporated, whisk until thick and creamy. Refrigerate for at least 30 mins.

Open and flip the 10-inch cake and lather the icing on top. Add the 7-inch cake on top and lather more icing.