For the walnut liqueur sauce, heat 150ml/5½fl oz of the walnut liqueur in a sauce pan and simmer until the volume of the liquid is reduced by half.
Add the remaining liqueur and stir in a pinch of xantham gum. Set aside to cool.
For the mousse, place the orange juice, white wine, honey, spices and orange liqueur in a saucepan. Bring to the boil, then reduce the heat and simmer until the volume of the liquid has reduced by two-thirds.
Place all the ingredients in an espuma gun and set the temperature to 50C/120F. (Alternatively, whisk the egg whites until soft peaks form when you remove the whisk and then gently fold in the orange mixture. Refrigerate until ready to serve.)
Preheat the oven to 180C/350F/Gas 4.
Butter and flour six 6cm/2½in soufflé ramekins.
In a food processor blend the panettone to fine crumbs.
Whisk the egg yolks with half of the sugar until thickened.
Place the white chocolate and butter in a bowl suspended over a pan of simmering water (alternatively use a microwave). Stir occasionally until the chocolate and butter are melted.
Place the egg whites and the remaining sugar in a bowl. Whisk with a handheld electric mixer until the mixture forms stiff peaks when the whisk is removed.
Fold the cooled, melted chocolate into the egg yolk mixture, then fold in the panettone and finally fold in the whisked egg whites.
Fill the moulds three-quarters of the way and bake in the oven for 6-7 minutes. Serve immediately with the mousse alongside and the sauce drizzled over.