Heat the oven to 170C/150C fan/Gas 5.

Butter a 28x10x8cm loaf tin, line it with baking parchment and butter the parchment, or use a loaf tin liner.

In a stand mixer or in a bowl using a hand mixer, or with a bowl and a wooden spoon, beat together the butter and sugar over a medium-high heat until very smooth, light and creamy, about 4 minutes.

Scrape down the bowl, and continue to beat while slowly adding the eggs.

In a separate bowl, sift or whisk together the flour, baking powder and salt.

Reduce the speed and gently beat or fold in the flour mixture until just combined.

Fold in the chocolate and walnuts.

Gently stir in the milk, coffee and vanilla and pour the batter into the tin.

Place the tin on a baking sheet and bake for 45-50 minutes, until a cake tester or a skewer inserted into the middle comes out clean.

Let the cake cool in the tin for 15 minutes before removing it and leaving it on a rack to cool completely.

While the cake is baking or cooling, make the frosting.

Chill the bowl and beaters in the fridge or freezer for 10 minutes before you start.

In a stand mixer, or using a bowl and a hand beater, whisk the mascarpone at a medium-high speed and when it is smooth slowly add the cream, beating as you go, until it’s combined and forms peaks that hold their shape.

Add the sugar, coffee and vanilla.

Cover and chill in the fridge while the cake cools completely.

Spread the frosting over the cooled cake.

Finish with the grated chocolate and walnuts.