Begin by spreading a generous amount of Nutella on two slices of thick bread. Top each with another slice to make two sandwiches.
In a bowl, whisk together the eggs, milk, vanilla extract, and ground cinnamon until fully combined.
Preheat a non-stick skillet or griddle over medium heat, adding one tablespoon of butter to melt and coat the pan.
Dip each Nutella sandwich into the egg mixture, ensuring both sides are well coated. Allow any excess mixture to drip off before placing it in the skillet.
Cook the sandwiches for about 3-4 minutes on each side, or until they are golden brown and crispy. Add more butter to the pan as needed for the second sandwich.
Once cooked, remove from the skillet and place on a plate. Dust generously with powdered sugar.
Serve warm, topped with fresh strawberries or sliced bananas, if desired.