Tear the loaves into large shreds, about 2x3/4 inches. To do this, pinch a piece of bread at the top of the loaf and start pulling. If the loaf is sliced, tear the slices. Spread the shreds on a large baking sheet and bake until lightly toasted, about 5 minutes. Remove from the oven and immediately drizzle melted butter over the bread. Sprinkle the cranberries over the bread. Top with remaining bread. Set aside.

In a heavy saucepan, heat the milk, cream, and sugar to a simmer. Off heat, add the chocolate and stir until melted and smooth.

In a medium bowl, whisk the eggs and vanilla. Add the chocolate mixture to the eggs, stirring until well blended. Pour the mixture over the bread, making sure the top layer of bread is completely moistened. Cover the pan loosely with a piece of foil. Bake for 15 minutes. Remove the foil and bake 15 minutes more, or until the pudding bubbles vigorously around the edges although the center is very liquid if the pan is jiggled.

Remove the pudding from the oven (it will continue to thicken) and cool on a rack. Serve warm, at room temperature, or cold, plain or with a dab of whipped cream or crème fraiche.