Whip Egg (3), Milk (1/4 cup), Vanilla Extract (1 teaspoon), and Ground Cinnamon (1/2 teaspoon) together until combined.
Crush Cap'n Crunch® Cereal (1 cup) and put it in a separate bowl.
Dip one slice of Brioche (4 slice) at a time, first into the egg mixture, and then into the cereal. Make sure it is coated well.
Transfer to a frying pan over medium heat with butter. Start with 2 tablespoons of Butter (4 tablespoon) and add more as needed. The pan should always be buttery to get your outer layer crispy.
Flip after about 2 minutes and repeat for all 4 slices of bread. Keep warm in the oven until ready to serve.