Heat the oil and butter in the pressure cooker. When the butter is foaming, add the squid and cook over a high heat until it is golden brown. Add the onion and garlic and cook for another 2 minutes. Add all the remaining ingredients to the cooker, season with the salt and black pepper, close the lid, bring to high pressure and cook for 20 minutes. Allow to release pressure naturally. Simmer for a couple of minutes then allow to rest for another 5 minutes before eating. Sprinkle with chopped parsley to serve.