While this recipe looks nice (with a caveat that the sauce looks too thick) you can achieve a perfectly good result by boiling a Bockwurst or two and then serving with Curry Gewürz Ketchup, although in my opinion it has to be Hela brand and has to the the 'sharf' variety. Curry powder may be sprinkled on top for added zest. Fried onions & chips are optional.
We always try to have Currywurst at least once when we visit Germany. My favourite take-away was at the top end of Holstenstraße by the St Nikolai Kirche in Kiel which we'd visit every time we were in town but it shut a few years ago much to our dismay.
Another classic from around that part of the world is take-away Danish Rødpølse hotdogs with remoulade, tomato ketchup & crispy-fried onion. It has to be bought in Denmark. Don't be fooled by German vendors' attempts - they never match up. (My other half says it's because the authentic Danish sausages aren't allowed in Germany but she may just be biased.) The best we've found so far are from Klostertorvets Pølsevogn in Nykøbing, Mors in Jutland. We often have one, go shopping and then have another they're so good.