You can buy squid tentacles from large supermarkets at the fresh seafood section.
To make them tender you have to boil them just like octopus tentacles. Know that during boiling the smell is quite strong but subsequently after cooking the aroma dissipates.
They need to be fresh, cook them the day you buy them. Don't freeze and leave them for the next day.
Put the tentacles in a pot, cover with water, add black pepper grains, bay leaf, an onion head and leave to boil. After the water comes to a boil, keep an eye on them because cooking times vary depending on the size of the tentacles.
The ones I bought were quite thick, they took 40 min. to cook but I've cooked tentacles before in half that time. Poke them with a fork occasionally in the thickest part - if it pierces them easily it means they're ready.
Be careful not to over-boil them because they tighten up and end up tough. If you do over-boil you'll have to boil them for at least 1 hour 30 min.
Take them out once ready, drain and wash away the ink under running water. Heat a grill or hot plate and roast the tentacles for 1-2 min.
Clean and chop the garlic. Heat the butter and olive oil in a pan, add the garlic and braise briefly. Pour in the wine, stir, season with salt and black pepper, pour in the juice of 1/2 lemon and cook about 1 min. until the alcohol evaporates a bit.
Once the liquid is reduced and sauce begins to thicken, chop the tentacles and add them to the pan. Stir and immediately remove from the stove. Serve with slices of lemon, plus dill or parsley.
The recipe was adapted from Pepa Stoeva.