Okay, so at the moment I'm looking into these three aspects of Italian cuisine. I've been having a look through the various extant menus supplied by some of the authors, to see how common dishes were and when they were served, beginning with Romoli. I've already noticed a few things that are interesting, and am developing some ideas that I need to look into further.
Romoli has the advantage that his book is aimed at the upper classes, but more rurally and at a lower level than, for example, Scappi. This means that his menus tend to be quite different to Scappi's, especially since he presents a year of day-to-day menus (from March 1546 forward), with a special meal (described as a Collation - "in the French style").
I'm only about four months through the menus so far, but am already having some interesting insights.
Looking for references to Mangiar Bianco, the first thing I noticed is that it doesn't show up a lot - unlike with Scappi, or Lancelotti. In fact, of the eight occurences I've come across so far, seven are from the Collations. The eighth was served as one of the antipasti on 28/07/1546. Two of the Collations have Mangiar Bianco served twice; once in the first course and one in the "Boiled" (Alesso) course.
Based on where this shows up in Romoli's menus, I'm pondering if Mangiar Bianco was a special feast day dish, rather than an everyday dish.
Furthermore, I'm also wondering if at least on some occasions, the white dish was bought ready made. Specifically, at least on the times (four out of eight so far) that it is served cold in tartlets. I'm wondering this for multiple reasons. Firstly, these always occur in a credenza course, course "posto in tauola" - i.e., laid on the table, or the antipasto course. We know already that the credenza courses are typically cooked by a separate kitchen to the cucina courses. For a household that is wealthy - but, unlike the Pope, not unseemly so - maybe they don't have a separate credenza kitchen. Also, from reading the recipes of an Italian apothecary (Leonardo Fiorauanti Bolognese), there is at least one example of someone outside of the role of cook preparing this dish (although in this case not in pie form). Maybe the tartlets were the equivalent of us popping into the supermarket or a bakery to pick up some mince savouries for a party.
With regards to menus presented in cook books, reading through Romoli's menus and comparing them to, for example, Scappi's, I'm thinking that difference in purpose may explain why we see such an abundance of variety in the recipes Scappi offers, compared to what he serves in the menus that he shares - after all, he only shares menus for fancy occasions, whereas Romoli is presenting day-to-day meals. Perhaps if Scappi had done a year of menus like Romoli's, we'd find out that the Pope ate beans most days.
I'm still pondering with Romoli how and when during the day I think the courses were served.
Regarding bean dishes, although not universal, they tend to be predominantly served on Lean Days. They're normally served as part of the "Fried" or "Boiled" courses - out of 37 instances so far, they are served 16 times as part of the fried course and 13 times as part of the boiled course. They show up as part of four Collations, and also make appearances in the Fruit (twice) and Antipasto (once) courses.
So far mushrooms are only served as part of Lean Day meals. They're usually served with a nut sauce, and sometimes with garlic. I wondered a while ago if our modern habit of cooking mushrooms with garlic dates from around this period, as at least one of the cooks (I can't remember off the top of my head which one) that supplies a recipe for them states to cook them with garlic to draw any poison out.
It has been interesting to notice that beans and mushrooms make almost no appearances on Romoli's menus for the months of June and July. Going forward, it will be interesting to see if there are other similar months and when these occur. I think that their scarcity is quite significantly because of the greater availability of other foods during these months, so they simply don't make the cut if you can eat them any time. With mushrooms, I am wondering if these are more seasonally gathered - I just don't know enough about mushrooms to draw any definite conclusion on this. It looks like fruit may put in more of an appearance during the Summer months, but I'm not currently focusing on that so will have to look into it more closely some other time.
The reason that I've ended up studying these three things at once is also worthy of note: it turns out that trawling a year's worth of daily menus is just not that exciting (even if the findings themselves are exciting), so it's at least more tolerable to be searching for several different items rather than going through one at the time!