With a spatula or butter knife, spread Nutella onto the four slices of bread, about 1 Tbsp per slice. (You can add more or less Nutella, based on your preference.)
Join 2 pieces of bread together, with the Nutella on the inside, creating a sandwich. Repeat with the other 2 slices of bread.
Whisk together the eggs, milk, cinnamon, vanilla, and sugar in a bowl or casserole dish.
In a large skillet, heat 1 Tbsp butter on medium high heat.
Take your sandwich and dip into the egg custard mixture, fulling dredging in the mixture. Do not over soak or the bread will become soggy.
Add the dredged sandwich into the heated skillet and repeat with the other sandwich.
Cook on medium high heat for about 2-3 minutes on each side, or until golden crispy.
Slice the bread in half or enjoy whole, top with desired toppings and serve immediately while still warm.