Preheat oven to 375F. Grease a 9×9 pan (do not flour).
In a small bowl, combine cranberries and soaking liquid. Let soak for 30 minutes, or cover with plastic wrap and heat in microwave for about 30 seconds (until very warm) to help berries rehydrate with bourbon. If microwaving, let mixture cool to room temperature before adding to the rest of the bread pudding mixture.
In a large bowl, whisk together milk, eggnog, eggs, sugar, nutmeg and vanilla. Add bread cubes and gently fold them into the mixture until all the custard has been absorbed. Stir in cranberries and remaining bourbon (any that hasn’t been absorbed into the cranberries but is still in the dish).
Pour into prepared pan, spread into an even layer and sprinkle top of loaf with additional sugar, if desired.
Bake 50-55 minutes, until a knife inserted into the center of the loaf comes out clean and the top is golden brown.
Allow to cool in pan and then transfer to a plate for serving.
Serve warmed. Store leftovers in the refrigerator.