Combine oil and sugar together in a medium-sized bowl. Whisk well to combine. Add the egg and vanilla; beat until lighter in color.
Sift in flour, cocoa powder, and salt. Gently fold the dry ingredients into the wet ingredients until JUST combined. Fold in the nutella.(Do NOT overbeat as doing so will affect the texture).
Spoon the batter into cupcake liners.
Bake for about 15 -20 minutes for just under-done. Should be very soft in the middle but not liquid or runny. Set them aside to cool to room temperature before serving.
Notes
Pro tip: If making fewer portions, beat the egg and only use what you need, save the rest for breakfast use if desired.