Slice the panettone through the equator into six thin slices. Set aside. For the buttercream, beat the butter, icing sugar, milk and vanilla together until smooth and creamy, then mix in the spices and orange zest.

Put the base slice of panettone on a serving plate and spread over a fifth of the buttercream. Scatter over a fifth of the hazelnuts, then top with another slice of panettone. Repeat until all the buttercream and hazelnuts have been used, finishing with the top slice of panettone. Dust over a little icing sugar before serving.