Begin by preparing the zabaglione. In the top of a double boiler or a heatproof bowl suspended over simmering water, beat the egg yolks and 3 tablespoons of the caster sugar until the mixture is thick and foamy. Gradually beat in 3 tablespoons of the Marsala wine. Continue whisking until the mixture forms a thick, creamy foam that coats the back of a spoon. Once the zabaglione is ready, allow it to cool slightly.

Meanwhile, in a separate bowl, whisk the egg whites with the remaining caster sugar until stiff peaks form. Gently fold the zabaglione and egg whites in small batches into the mascarpone cheese until smooth and well combined.

Combine the coffee and remaining Marsala in a mixing jug.

Create a layer of the panettone slices in your serving dish, spooning some of the coffee mixture over the top and a sprinkling of the coca powder. Then coat this in a generous portion of the zabaglione-mascarpone mixture. Continue layering until all ingredients have been used, finishing with a layer of zabaglione-mascarpone and a final dusting of cocoa powder on top.

Allow the tiramisu to set in the fridge for several hours, preferably overnight, before serving.