Preheat a large griddle or pan over medium low heat. We want it low and slow here so all the egg gets cooked.
In a medium bowl, whisk together eggs, milk, vanilla, and sugar.
Pour egg mixture in a 9x13 casserole dish, or split between some big, shallow vessels.
Place the outer part of the croissant halves in the mixture, making sure the entire surface gets wet.
Next, flip them over so the nook-and-cranny parts are face-down, ass-up in the liquid. Gently press down on each halve so when they bounce back up, they suck up the juices.
Let rest for at least 5 minutes. When time is up, flip over one more time and spoon any excess egg into the croissants' holes.
Grease or butter your griddle. Place croissant halves outside-down onto the surface. Sprinkle tops with cinnamon. Cook for at least 5 minutes or until desired golden browness is achieved. Flip over and repeat, this time no cinnamon.
Serve immediately with your choice of toppings...a fried egg here is AMAZING. That sensual, savory yolk is the perfect contrast to this sweet dish.