Whisk the eggs with the vanilla extract, milk, sugar and cinnamon in a shallow dish. Place the slices of bread in the mixture, turning to coat both sides so that they absorb the liquid.
Heat the butter in a nonstick frying pan. Use a palette knife or fish slice to transfer the soaked bread to the hot pan and fry for 2 minutes on each side until golden.
Cut the toasts in half diagonally, sprinkle with a little caster sugar and serve immediately.