Wash your glass jars and screw tops in (ideally) boiling (but in practice almost boiling) water with a handful of washing soda dissolved in it. Rinse in very hot clean water and upend the jars on a clean cloth, for instance a tea-towel, to drain.
Put the tomatoes in a bowl large enough to cover them completely with water. Pour boiling water over to cover. Wait for half a minute. Pour the water off and rinse the tomatoes under a cold tap or plunge them into cold water. The skins will now come off easily.
This also works for slightly underripe peaches or apricots.
This is a fiddly business, not hard but messy and slightly icky. If you're squeamish (or lazy or pressed for time) you can buy your squid ready-cleaned, but then you won't have the tentacles, which are the best part.
Take a squid in one hand and pull firmly but gently at the head with the other hand until the head comes off. If you're lucky, the intestines will come with it. Cut the tentacles off just behind the eyes, so they stay in a bunch.
Rub and peel the purplish skin off the body (this goes best under a cold tap) until you have a white smooth sack-like object. The fleshy "fins" are edible, but if it's too much trouble to preserve them it doesn't matter much. Pull out the transparent plastic-like "pen" (calamus; that's why they're called 'calamari') and press out all other goo and strange objects. Rinse out the sack-like object (tube) and either leave it whole to stuff or cut it into pieces or rings.
Repeat until you run out of squid. Drain and dry with kitchen paper.
I spent far too much time struggling with teaspoons before I realised that squid tubes are easiest to stuff with a normal plastic household funnel and the handle of a wooden spoon.
Boil the same weight each of crystallised sugar and water (for instance 300 ml water and 300 g sugar) until the syrup is clear and no longer foams. Pour it into very clean bottles or jars. It will keep in the fridge for a month or more.
Make a shallow incision halfway up the side. Lay a string around the cake in the incision. Cross the ends and pull apart slowly and steadily until the string has got through the cake completely. If you want three layers, cut the lower one first.