I've mentioned this piece of kit before, in passing, but I didn't know at the time whether it was still available, and if so how widely. This is an integrated double boiler, or bain marie, where an opening in the top of the handle allows you to fill the base of the pot with water, which when heated then acts as a bain marie for the top part of the pot. I first came across this invention sometime in the eighties, in Divertimenti in Fulham Road; it was then made by a German company, it was called (appropriately enough) a zimmertopf, and cost the sort of price you'd expect from Divertimenti. I've never had to replace one (I have one in each kitchen - hence 'essential'), and so was uncertain whether they were still around, and whether they still cost an arm and a leg. They are and they don't!
A cursory look around the internet found them at both Amazon and an outfit in the US called, I think, Gourmet Kitchen. Much more reasonably priced than I recall, as well, at around $50/£27. I suspect they aren't called 'zimmertopfs' any more though, so some creative thinking might be needed in tracking down the exact item from the stockists' list.
Nothing ever burns or gets lumpy in this pot. You can make things like Creme Patissiere, or Hollandaise and be remarkably relaxed about doing other things at the same time, and merely returning from time to time for the requisite stir and to see how near 'done' it is. Excellent for melting chocolate, or butter, or apricot paste..... you probably get the gist.
I think I once - about ten years or so ago - had to replace the little glass element in the base of one of the handles - through which you can gauge whether or not the water needs to be refilled - and the replacement piece cost about three pounds and arrived with German efficiency in about three days from ordering. The in-house technical department (i.e. bloke here with a screwdriver) made the substitution in about ten minutes, and all was as good as new.
Celery Risotto. (The Italian Celery has a flavour about five times as intense as that you normally find in the UK!)
Breast of Chicken, with a Lemon and Caper Sauce.
Poached Pears on a Prosecco Zabaglione.