F_C – bottle of cheap gin, empty out about half of it, half-fill bottle with sloes (you need to break the skin – see below) then about 150g of sugar, top up with gin, put the top on and shake. Put it in a dark cupboard and give it a good shake about once a week. Start tasting at about the 3 month mark once sugar is all dissolved. Leave no longer than 6 months. Decant, let it settle and syphon off and leave the sediment. Enjoy.
Take the gin-soaked sloes and bung in some scrumpy cider, leave for a week. Enjoy slider!
Breaking the skin – some use pins, some a fork. Too much effort. I freeze the sloes until I need them, then run a batch under the hot tap – that defrosts them and breaks the skin.
If you want to make a lot, use demijohns or something bigger – same proportions. I made 4 gal last year in a home brew barrel! Damson gin is very similar if you have them local too.