The day before, start with the crème anglaise. In a small saucepan, add heavy cream, milk, vanilla bean seeds with pod or vanilla bean paste. Bring to a boil over medium-high heat. Cover with a lid and turn off the heat. Let it sit for about 30 minutes.
Meanwhile, in a large bowl, fill with ice cubes. Set aside a smaller bowl that can hold the finished cream and fit on top the bowl of ice.
In a medium saucepan, whisk together egg yolks and sugar until pale yellow. While whisking, slowly pour in ¼ of the hot cream mixture. Once combined, add the rest of the cream in a steady stream. Remove and discard bean pod if using. Return the saucepan to the stove and set over medium heat. Cook until reaches 180˚F (82˚C) or the mixture thickens enough to fully coat the back of a spoon. Remove from heat. Pour the cream into the smaller bowl. Set the bowl into the ice bath (larger bowl with ice). Stirring frequently until the mixture is cool completely. Transfer the cream to an air-tight container. For best result, chill in the fridge for 24 hours.
For the bread pudding, preheat the oven to 350˚F (177˚C). Place a large piece of aluminum foil on the oven rack to catch any dripping. Grease a 2-cup baking dish with ½ tablespoon unsalted butter.
Cut the croissants into ½-inch slices lengthwise with a sharp serrated knife. Layer the croissant slices into the baking dish. If needed, cut into smaller slices to fit better. Place the blueberries in between the slices.
In a medium bowl, whisk together heavy cream, whole milk, vanilla extract, eggs, sugar (except for turbinado sugar). Carefully pour the custard over the croissant & blueberries until the batter almost reaches the rim of the baking dish. It may take a few minutes for the croissant to absorb all the liquid. It’s perfectly ok that the top part of the croissant is not submerged. Sprinkle the turbinado sugar all over the pudding.
Bake in the oven for 40 to 50 minutes, or until the pudding puffs up and the custard is set. Remove from oven and let cool for 10 minutes. Dust with powdered sugar and serve warm with crème anglaise.
