Preheat the oven to 180C /350F and line a large loaf tin with baking paper.

Mix the instant coffee with the water and dissolve.

To make the crunchy topping, bash up the biscuits by hand in a Ziploc bag using a rolling pin, or pulse in a food processor to get a rough textured crumble.  Add the melted butter and mix well.

To make the cake, put the butter and caster sugar in a bowl and use an electric mixer to beat until pale and fluffy. Add each egg one at a time ensuring you mix well before adding the second egg. Add the vanilla extract and coffee mix and whip to combine.

Sift the flour and cocoa powder and then alternate by adding this with the buttermilk to the cake mix. Do not overbeat.

Scrape down the bowl and pour half the batter into the prepared loaf tin.

Sprinkle half the crunchy topping mix over the batter and lightly press it to smooth down. Top this with the remaining batter and spread this across the tin.

Sprinkle over the remaining crunchy biscuit topping mix and bake for 60 minutes until firm to the touch and when a sharp knife comes out clean. Loosely cover the loaf with tin foil or baking paper from about halfway through the baking time to prevent over-browning.

Set aside on a cooling rack to cool.