Start by trimming the crusts off the bread slices. If the bread is very fresh, handle it carefully to avoid tearing or crumbling.
Spread Nutella on one side of each bread slice. Place one slice on top of another to make a sandwich. Once stacked, cut each sandwich in half to create 6 sticks.
In a medium-sized bowl, whisk together the egg, milk, and vanilla extract. Dip each Nutella stick into the mixture, turning it to ensure all sides are evenly coated. Don’t leave it in the mixture for too long to avoid making it too soggy, and make sure the corners are fully covered!
Heat a skillet over medium-high heat and melt a bit of butter. Place the Nutella sticks in the skillet and fry for about 2 minutes on one side, then flip. If your bread is very thick, make sure to fry the sides as well—about 30 seconds per side. If your bread is thinner, like mine, this step won’t be necessary!
While the Nutella sticks are cooking, mix the cinnamon and sugar in a shallow plate until well combined. Once the sticks are done frying, toss them in the cinnamon sugar mixture, ensuring they are evenly coated on all sides.