Score the squid sheets by taking a skinned and gutted squid, wash the cleaned squid hood under cold running water. Drain. Remove and discard the clear, hard quill from inside the hood. Use a sharp knife to cut the hood lengthways from opening to tip. Lay the hood flat, inside up, on a clean work surface. Score the hood in a diamond pattern don't cut all the way through though).
Heat the oil in a frying until smoking. Add the squid and toss over a high heat for 30 seconds until brown and the squid has lost its translucency. Lift onto a plate.
Add the onions, cherry tomatoes and garlic to the pan, and stir over a medium heat for three minutes. Add the Cava, bring to the boil and allow to reduce, by boiling, to half the original quantity.
Stir in the crème fraiche and basil, bring back to boil simmer until the sauce starts to thicken. Remove from the heat, season with salt and pepper and return the squid to the pan. Serve with rice or noodles