To Make the Chocolate Soup:
Use a vegetable peeler to remove the orange zest, leaving the bitter white pith behind. In a large saucepan, combine the orange zest, milk, and half-and-half. Heat over medium heat until it reaches a simmer, with bubbles forming along the sides. Remove from heat, cover, and let the mixture steep for at least 30 minutes or up to 2 hours, depending on the desired intensity of the orange flavor.
While the milk is infusing, finely chop the semi-sweet chocolate. In a small bowl, mix the cornstarch and cold water until the cornstarch is completely dissolved. Place the egg yolks in a separate medium bowl.
After the milk mixture has infused, return the pan to medium heat and warm it until it’s nearly simmering (hot but not boiling). Whisk in the chopped chocolate until fully melted. Add the cornstarch mixture and whisk to combine.
Gradually whisk the egg yolks while slowly drizzling in about 1 cup of the hot chocolate milk mixture to temper the eggs and prevent them from curdling.
While continuously whisking the chocolate soup in the pan, slowly drizzle in the tempered egg yolks. Add the salt and vanilla extract, and continue cooking the soup, whisking frequently, until it thickens slightly and reaches a creamy soup-like consistency.
Serve the soup warm, topped with croissant croutons and a dollop of whipped crème fraiche.
To Make the Croissant Croutons:
Preheat the oven to 300°F (150°C) and line a baking sheet with aluminum foil.
Cut the croissants into small cubes. In a large bowl, melt the butter in the microwave, then toss the croissant cubes in the melted butter to coat.
In a small bowl, mix together the granulated sugar and ground cinnamon. Sprinkle the cinnamon-sugar mixture over the buttered croissant cubes and toss to coat evenly.
Spread the coated croissant cubes on the prepared baking sheet and bake for 15-20 minutes, stirring every 5 minutes, until the croutons are lightly golden and crunchy. Let them cool completely.
To Make the Whipped Crème Fraiche:
Chill a mixing bowl and whisk attachment in the refrigerator for 15 minutes.
In the chilled bowl, combine the heavy cream, crème fraiche, powdered sugar, and vanilla bean paste or extract. Beat on medium-high speed, scraping down the sides of the bowl as needed, until the mixture thickens and holds firm peaks. Be careful not to overbeat, as it can become grainy.