Lightly grease the inside of the slow cooker. Place the bread cubes inside.
In a mixing bowl, whisk together the eggnog, eggs, granulated sugar, vanilla extract, nutmeg, and cinnamon until smooth.
Pour the mixture evenly over the bread cubes. Press down gently so all the bread soaks up the liquid.
Cover and cook on low for 3 to 4 hours, until the center is set and no longer liquid.
When the bread pudding is nearly done, make the sauce. In a small saucepan over medium heat, melt the butter with the brown sugar.
Stir in the heavy cream and bourbon. Simmer for 3 to 4 minutes, stirring often, until the sauce thickens slightly.
Spoon the warm bread pudding into bowls and drizzle with the bourbon caramel sauce before serving.