Butter a deep 9x12 baking dish and preheat the oven to 375°F
Cut up the croissants into cubes slightly larger than croutons.
Add the cubed croissants to the baking dish and sprinkle the blueberries on top.
With an electric mixer (with paddle attachment) cream together the room temperature butter and sugar. Add the vanilla. Mix in the eggs one at a time.
Pour in the heavy cream, whole milk and vinegar. If you want the lemon zest, add it here and mix until combined, scraping down the sides. The mixture may look like it is curdled or not all mixed together. That is ok.
Pour the milk and sugar mixture evenly over the blueberries and croissant cubes, making sure to scrape the bowl for any missed sugar and butter.
Sprinkle another 2 tablespoons of sugar over the top.
Bake uncovered for about 45 minutes or until a knife inserted in the middle comes out clean and the croissant cubes on the sides are golden brown. Serve warm