Jerusalem Artichokes with Avocado Hollandaise

Dunno if it’s just me, but Jerusalem artichokes always make me sit up straight and mind my aitches. This is daft, as in many countries they are regarded as being fit only for cattle: I must have eaten them somewhere very smart in my formative years. I am also slightly in awe of Brussels sprouts: my father was apparently force fed so many at school during WWII (rationing, remember?) that they were taboo in our house when I was a nipper. Anyway, teaming these vegetables with avocado hollandai