How to Make It
Bring the cream, milk and sugar to a boil in a small, heavy saucepan over moderate heat, stirring frequently. In a small bowl, mix the amaretto and cornstarch to blend, then whisk it into the cream mixture. Simmer over moderately low heat, stirring constantly, until the sauce thickens, about 2 minutes. Keep warm.
Lightly butter a 13-x 9-x 2-inch baking dish. Spread the panettone cubes in the prepared dish. In a large bowl, whisk the eggs, cream, milk and sugar to blend. Pour the custard over the panettone, and press the cubes gently to submerge them. Let stand for 30 minutes, occasionally pressing the panettone into the custard.
Preheat the oven to 350°. Bake the pudding until it is puffed and set in the center, about 45 minutes. Cool slightly. Spoon the bread pudding into bowls and drizzle with the warm sauce.