Mix together the white and brown sugars in a small bowl.
Pour half the sugar mixture into a separate mixing bowl and blend with butter, orange zest and orange juice.
Spread the butter mixture on one side of each slice of bread. Cut each slice of bread in half diagonally. Arrange the bread triangles in an overlapping fashion in an 20x20cm baking tray with the buttered side down.
Place the remaining sugar, grated chocolate, milk, cream and eggs into a blender then blend until thoroughly mixed.
Pour the chocolate mixture over the bread making sure to evenly cover it. Cover and refrigerate the prepared dish for 1 hour.
Preheat an oven to 180 degrees C.
Bake until golden brown and set; 30 to 40 minutes.