1. In a large, shallow dish, whisk together eggs and milk; set aside.
2. Form two sandwiches with the bread and chocolate (break chocolate as necessary to cover bread without extending over edges); dip both sides of sandwiches in egg mixture to coat.
3. Heat butter in a large skillet over medium heat; transfer sandwiches to skillet. Cook, pressing occasionally with a spatula, until golden, 1 to 2 minutes per side. Transfer to a paper towel-lined plate. Cut in half, and dust with confectioners’; sugar before serving.