Melt Chocolate over baine-marie, then add Oil.
Add Butter, then Nutella and stir till melted and uniform.
Whisk Eggs, Yolk and Sugars in mixer till doubled in size.
Pour cooled chocolate mixture into whisked egg mixture.
Whisk in dry ingredients and mix till combined.
Pour entire mixture into a greased 9x13" pan.
Bake @325f (162c) for 35mins - check with toothpick.
Cool 1hr before cutting into squares.