Heat oven to 325° F.
Place the panettone in a large bowl. In a medium bowl, whisk together the cream, milk, eggs, yolks, sugar, zest, and vanilla. Pour over the bread cubes. Let soak for 5 minutes, stirring gently 2 or 3 times. Pour the mixture into a buttered 9-by-13-inch baking dish. Bake for 60 to 70 minutes. Serve warm.
Tip: Panettone (a light, sweet Italian bread made with nuts and candied fruit) is available at most grocery stores during the holiday season. Or use challah or brioche instead and sprinkle in a handful of raisins.