Grease the inside of your slow cooker with cooking spray or butter.
In a large mixing bowl, whisk together the eggs, milk, heavy cream, brown sugar, vanilla extract, ground cinnamon, and salt until well combined.
Add the cubed bread to the egg mixture and gently fold until all the bread is coated. If using, fold in the chopped nuts and dried fruit.
Pour the bread mixture into the prepared slow cooker, spreading it evenly.
Cover and cook on low for 4 to 5 hours, or until the center is set and the edges are golden brown.
Once cooked, turn off the slow cooker and let the French toast bake sit for about 10 minutes before serving.
Serve warm, dusted with powdered sugar if desired.