Dense espresso and walnut brownie

Place the butter and half of the sugar (100 g) in a saucepan over low heat. Heat until the butter is completely melted and forms a fluid mixture, then simmer gently for 1 minute until the sugar crystals are almost dissolved.

Remove the saucepan from the heat, add the dark chocolate broken into pieces and stir continuously — the residual heat will melt the chocolate completely, forming a glossy cream.

Allow the chocolate mixture to cool to room temperature, then fold in the 30 ml of brewed espresso coffee.