Butter a standard loaf pan, or spray with cooking spray. If you want the pudding to come out whole add a piece of parchment to the pan as well.
In a large bowl whisk together the eggs, milk, sugar and cinnamon.
Cut the brioche into 1/2-inch thick slices and dip into the egg mixture.
Place 1 layer of soaked brioche pieces into the pan, then alternate with chocolate and butter.
Add another layer of bread, then chocolate and butter. Do this until all the bread is used up.
Pour the remaining milk mixture over the pan.
Cover and refrigerate for 2 hours.
Preheat oven to 300 and bake for 1 hour.
Garnish with chocolate, a drizzle of Bailey's, and whipped cream.