Cut the panettone into rough chunks and arrange in a deep roasting dish (you want them to be quite snug and compact).
Heat the cream until just about to boil.
Whisk the eggs, yolks, caster sugar and pistachio paste together with the vanilla until smooth and well combined. Pour the hot cream on top, whisking well. Pour the mixture over the panettone.
Chop the pistachios and sprinkle over the top along with some demerara sugar.
Bake for 30 minutes, or until golden and just set in the middle. You can cover with foil if the centre is still too soft but the top is beginning to colour too much.
Notes
Substitutes:panettone – brioche; pandoropistachio paste – very finely ground pistachios (although the flavour won’t be as intense and they will add texture to the custard)