Pre heat the oven to 160°C
Spread the butter onto the panettone, then the marmalade and then cut in half.
Bring the milk, cream, vanilla, orange zest, half of the sugar, and salt to a simmer, then leave for 15 minutes.
Whisk the eggs with the rest of the sugar.
Re-simmer the milk and cream before pouring into the eggs, then pass through a fine sieve.