Preheat the oven to 325°F (165°C). Generously butter a 12-inch (33-cm) round or 9-by-13-inch (23-by-33-cm) baking dish.
Spread the challah slices thickly and evenly with the butter. Cut the slices in half crosswise. Lay the slices in the dish so that they overlap slightly.
In a bowl, whisk together the whole eggs, egg yolks, milk, cream, sugar, salt, vanilla, cinnamon, and nutmeg. Pour evenly over the bread. Let stand for about 30 minutes so that the bread soaks up the egg mixture, occasionally pressing down on the slices with a spatula.
Bake the pudding for 30 minutes. Meanwhile, gently warm the marmalade in a small saucepan over medium-low heat. Remove the pudding from the oven and carefully spread the marmalade over the top. Continue to bake until the top is crisp, brown, and sticky, about 10 minutes. Let stand for about 10 minutes. Serve garnished with whipped cream.