Often, being in the middle of a PhD can feel a bit like eating a steak: there's a lot of it, and it takes dedication to get through it all (one could extend the metaphor further and say that depending on the cook it can be dry in places and succelent in others...). There's certainly no flitting between small nibbles of different flavours and textures. In general, I prefer and do find focussing on a single topic or thesis-related task; ideally I think I need a good two or three weeks of just concentrating on one area - on which I may already have done research in a more disparate fashion - before I can even start to write the chapter on it.
But, that requires a lot of concentration, and after a fairly long break hosting family, my concentration muscles are a bit out of shape. I'm not mentally prepared, just yet, for getting down into the meat of a chapter topic. So, instead, I'm in the middle of a lovely day of what I'm going to call smörgåsbord studying. I've been going back to the mental to-do list of all of the small holes that I have yet to fill in, across all of my research for all of my different chapters, and have been drawing up reading lists and perusing articles on a whole range of topics. I started with early modern mining (which will be part of chapter four), which led me onto an edited volume about geology and the scientific revolution (chapter two), then tracked down a couple more early modern travellers to mountainous regions (chapter three), and right now am looking forward with anticipation (and mild terror) to delving into the extraordinarily broad life and thoughts of Athanasias Kircher, an eccentric polyglot in the full sense of both words (who will also feature in chapter two).
Obviously this sort of approach is not sustainable - I wouldn't have chosen, even in my childhood enthusiasm, to live off choosing teas every night - but every now and then it can be a refreshing break from the mentally filling work of knuckling down on that chapter on that topic. And, you know what? It's made me remember just what it is that attracted me to my thesis topic in the first place - that it includes, to continue the metaphor, some pretty delicious stuff.