Whisk together the eggs, half and half, vanilla, cinnamon, and sugar. Submerge the croissant halves one at a time, turning them several times to ensure they soak up a lot of the batter. I like to push them down in the batter once on each side to fully submerge them.
3 large eggs, 1/2 cup half and half, 2 tablespoons granulated sugar, 2 teaspoons vanilla extract, 1/2 teaspoon cinnamon