01 - Preheat oven to 350°F. Grease a 9 x 13 inch baking dish with softened butter.
02 - Distribute panettone cubes evenly into the prepared baking dish.
03 - In a large mixing bowl, vigorously whisk eggs, granulated sugar, whole milk, heavy cream, vanilla extract, orange zest, and cinnamon until fully blended.
04 - Pour custard mixture over panettone cubes, ensuring all bread surfaces are covered. Gently press the bread to absorb the liquid.
05 - Dot the surface with the remaining butter. Allow mixture to rest for 10 minutes, permitting the panettone to soak thoroughly.
06 - Bake for 35 to 40 minutes until custard is set and top is golden brown.
07 - Remove dish from oven and let rest for 10 minutes. Lightly dust with powdered sugar prior to serving.