Preheat the oven to 350F.

Slice your panettone in thick slices, and lay them in a single layer on a baking sheet. Bake for 8-10 minutes, then flip and bake for about 10 minutes longer. You want the panettone to be dry to the touch and lightly toasted.

Remove pan from oven and set aside.

Lightly butter a 9x13 baking pan, and arrange the panettone slices inside.

In a medium bowl, whisk together the eggs and milk until well-combined. Pour on top of the panettone slices.

Sprinkle the turbinado sugar on top. If you have the time, let the slices soak in the mixture for at least 30-45 minutes (you can even do overnight!). If not, go straight to baking.

Bake at 350F for 40-45 minutes, until the eggs are cooked through and casserole has solidified.

Serve immediately with maple syrup!