Break the coconut fat into pieces and let them melt at low temperature. In the meantime, mix the instant coffee, cocoa, powdered sugar, salt, eggs and rum in a baking bowl. When the fat has melted, cool it and then add it to the quantity.
Then line a loaf pan with parchment paper and alternate layers of the quantity and the cookies.
Put in the fridge for 2-3 hours, then turn the cake out onto a plate and off you go.