For the gingerbread:

1. Preheat the oven to 350 degrees. Lightly grease a loaf pan with butter.
2. In a medium mixing bowl, add flours, baking soda, salt, and spices and stir to combine.
3. In a large mixing bowl (or stand mixer), beat butter and molasses until combined. Add eggs and ginger and beat until combined. Alternate adding flour and buttermilk to the wet mixture, a little at a time, so that you begin and end with the flour. Stir until combined.
4. Transfer the mixture to the loaf pan and bake for 45-50 minutes, or until a toothpick inserted in the middle comes out clean. Turn out onto cooking rack to cool completely.
5. Cut loaf into cubes to let dry out overnight.

For the bread pudding:

1. Preheat oven to 325 degrees.
2. Transfer cubed gingerbread to a large baking dish. In a medium bowl, whisk eggs, milk, sugar, and vanilla until combined. Pour wet mixture over bread into the baking dish. Sprinkle raisins over top.
3. Bake for 50-55 minutes or until pudding has set.
4. Let cool for at least 10 minutes. Serve warm with eggnog sauce.

For the eggnog sauce:

1. In a small saucepan, whisk together sugar, cornstarch and salt over medium-high heat. Slowly pour in eggnog, whisking constantly. Whisk frequently until sauce comes to a boil and thickens. Serve warm with bread pudding.