If using fresh bread, lay the slices on a cookie sheet in a single layer and bake in a 220 degree oven for 30-45 minutes or until they are crisp but not brown. Alternately, leave the bread on the cookie sheet in a cold oven for 4 or 5 days. In either case you then cut the slices into 1 inch pieces and set them aside.
Grease an 8” square glass baking dish with just enough butter to coat the inside bottom and walls. Melt the remaining butter and set it aside to cool slightly.
In another bowl beat the eggs until well blended then whisk in the cornstarch, baking powder, eggnog, and melted butter. If your eggnog is not very sweet (different brands vary) or if you prefer an extra sweet bread pudding then add up to ¼ cup of sugar.
Place the bread in the greased baking dish and pour the liquid over them. Gently slide the bread pieces around so that they are evenly coated with the liquid. Some corners should break the surface of the liquid.
Place the mixture in a 350 degree oven for 40-45 minutes or until a toothpick inserted in the center comes out clean and the top of the pudding has browned.
Allow to cool slightly then sprinkle the top with a few shakes of nutmeg (for an authentic Eggnog taste or with cinnamon if you are feeling less adventurous.
Serve warm or refrigerated.