Lightly butter an 8-inch square baking dish. Spread the bread cubes in it.
In a bowl, whisk together the eggs, brown sugar, vanilla, cinnamon, nutmeg and salt until well blended. Pour in the milk and whisk until combined. Pour the mixture over the bread cubes. Let stand, pressing down on the bread occasionally, until it is evenly soaked, about 20 minutes.
Meanwhile, preheat an oven to 350°F.
Scatter the cranberries evenly over the surface of the soaked bread and press to submerge the fruit. Set the baking dish in a large, shallow roasting pan. Add very hot tap water to the roasting pan to come halfway up the sides of the baking dish.
Bake the pudding until a knife inserted near the center comes out almost clean, 45 to 55 minutes. Serve warm or at room temperature. Generously dust the top of each slice with confectioners' sugar. Serves 8.