Spread nutella in the center of 4 of the pieces of bread, and assemble each like a sandwich. Don't spread it all the way to the edges so that the edges of the bread will adhere together later with the egg mixture.

In a shallow baking dish (with sides), whisk the eggs and the milk together.

Dip each sandwich into the egg mixture and flip it over a few times to saturate the bread.

Heat butter in a large skillet over high heat. Cook each piece until golden brown on both sides. (a minute or 2). Dust with powdered sugar and serve.