For the bread pudding lightly butter a 9 by 13 by 2-inch baking dish. Cut 1 pound or a little more Panettone into 1-inch cubes. Place them in the bottom of the baking dish. In a large bowl, whisk 8 large eggs,1 1/2 cups heavy cream, 2 1/2 cups whole milk and 1 1/4 cups sugar. Pour the custard over the bread cubes and press the bread gently to submerge. Let stand for 30 minutes, occasionally pressing the bread cubes into the custard mixture.
Preheat the oven to 350 degrees F and bake the pudding until it puffs and is set in the center, about 45 minutes. Cool slightly. Spoon the bread pudding into bowls and drizzle with the warm sauce.
You can make a head a refridgerate. Cut and reheat individual slices topped with sauce in the microwave.
To make the sauce bring 1/2 heavy cream, 1/2 cup whole milk, and 3 tablespoons sugar to a boil in a small saucepan over medium heat, stirring frequently. In a small bowl, mix 1/4 cup Amaretto and 2 teaspoons cornstarch to blend, then whisk it into the cream mixture. Simmer over medium-low heat, stirring constantly, until the sauce thickens, about 2 minutes. Keep warm or refrigerate up to 3 days.