Not-Plan Get Cookbook
[ ] [LIBRARY] Barak Varr booksellers: Cooking, two other topics.
[ ] [PURCHASE] Books on cooking: Extensive and Esoteric Halfling (250gc), Extensive and Esoteric Bretonnian (250gc)
If I'm understanding the option correctly, each topic from the Barak Varr booksellers gets us all the Imperial and Dwarven books on a topic. For a topic we don't have Imperial or Dwarven books on, that's enough books for a +10 bonus. Add to that out-of-pocket purchases of both Bretonnian and Halfling cooking books for a massive +20 bonus. (Of all the topics Halflings might have unique books on outside the Imperial catalogue, I'd think cooking is almost certain to be one of them.)
Yes, it's expensive. But cooking and cookbooks are likely to be a popular topic in the local community in a way that most scholarship wouldn't. Certainly Panoramia would appreciate an entire library section dedicated to cooking. And a +20 bonus is high enough that even if Mathilde rolls totally bogus again, she'll still be able to make a decent enough book. (And atone for her sins.)
The only thing this doesn't get is Eonir books. I'm not sure if Mathilde can purchase those out of pocket or not. If she can't, I don't think it's worth waiting a second turn just to get another +5 of books. Even if the Eonir are more likely to cook with magical ingredients than most. And the other alternative is worse:
Not-Plan Maximum Over-Cookbook
[ ] [LIBRARY] Library of Mournings: Cooking, one other topic
[ ] [PURCHASE] Books on cooking: Extensive and Esoteric Imperial, Dwarven, Halfling, and Bretonnian (1000gc)
Here, we'd get the maximum possible +25 of cookbooks. But we'd also get one less other book topic, and we'd spend 1,000gc out of pocket. We might not even have 1,000gc next turn, depending on who the Worst Slayer is. I don't recommend this Not-Plan, and only put it here for demonstration.
/madness