Cut panettone into large slices. Place into a buttered baking dish so that they fit snugly.
Mix eggs, milk, sugar, and vanilla extract together in a large bowl. Pour this mixture over the panettone. Cover the baking dish in saran wrap and place it in the fridge overnight.
When you're ready to eat your panettone, take it out of the fridge and preheat the oven to 350 F.
Once the oven is heated, place the baking dish inside the oven and bake for approx 45 mins or until golden brown and all the custard has absorbed into the panettone.
Feel free to top with whipped cream and maple syrup!