Preheat the oven to 350°F.
Cut top off squash to create a bowl, and remove seeds and insides (save seeds for roasting).
In a small bowl, stir together 1/4 cup of the brown sugar and 1 Tbsp cinnamon. Then dust the inside of the squash with this mixture.
In a large sized bowl, whisk together eggs, milk, whipping cream, remaining brown sugar, salt, cinnamon, nutmeg and vanilla in a large bowl. Fold in bread cubes and optional add ins, and let soak for 10 minutes.
Spoon bread mixture into the squash, making sure to pour in all liquid, and place on a lined baking sheet.
Loosely cover with tin foil and bake for 50 minutes. Remove the foil and bake for another 10 minutes until squash is tender, and bread pudding is set (caker tester comes out clean).