Toss cleaned octopus in cornflour, salt and pepper until well coated. Shake off excess and place on a plate until required.
Heat vegetable oil to 190⁰C and pan fry octopus until crispy and golden. Drain well on a paper towel-lined plate. Season with salt and pepper to taste.
For mayonnaise, whisk eggs and vinegar until pale and emulsified. Slowly add grape seed oil in a thin stream whisking continuously until thick. Season with salt and pepper to taste.
To serve, arrange squid on a serving plate with a bowl of mayonnaise on the side.