For the bread pudding: Using a serrated knife, hollow out the boule. Cube the hollowed-out bread into 2-inch pieces and put in a large bowl. Using your fingers or a spoon, scrape any remaining bread from inside the boule to create a crusty bowl. Add any scraped bread to the bowl along with the bread cubes.
In a medium pot, gently heat the milk, cream, butter, granulated sugar and vanilla paste until the butter is melted and the sugar is dissolved. Let cool completely.
Add the eggs to the milk mixture and whisk until combined. Pour the custard over the cubed bread, stir in the chocolate chunks and let sit for 45 minutes to 1 hour.
Preheat the oven to 350 degrees F.
Line a baking sheet with parchment and spray with nonstick spray. Place the boule on the baking sheet. Pack the custard/bread mixture into the bread bowl. It will protrude a bit--that's a good thing! Mix together the demerara sugar, cinnamon and salt in a small bowl. Sprinkle the mixture on the top of the bread pudding. Bake until golden and crusty, 40 to 50 minutes. Let cool slightly.
For the whipped cream: In a cold bowl, mix together the cream, granulated sugar, cinnamon, vanilla paste and salt. Beat to medium peaks.
Cut the bread pudding into "slices" and top with the whipped cream.