In a shallow dish; combine the egg yolk, half and half, and vanilla.
Spread 1-2 tablespoons of Nutella on 4 slices of bread (all the way to the edge). Place other 4 slices on top to form a sandwich.
Heat a large skillet over medium to medium high heat. Add a tablespoon (or so) of butter to heated skillet.
Once butter is melted, dip each sandwich into egg mixture. And place sandwich into skillet. Cook for about 4-6 minutes per side, or until golden browned on both sides of sandwich.
Serve Nutella Stuffed French Toast warm and topped with a sprinkling of powdered sugar and fresh chopped strawberries.
Note: If using a thicker bread or the bread has become too saturated with egg mixture, place browned stuffed french toast on a baking sheet and place into a 350 degree F oven. Bake for an additional 10-12 minutes until bread has fully cooked. (Also a great way to keep sandwiches warm if feeding a crowd!)