The Sweetness at the Bottom of the Pie is the first in the Flavia de Luce series by Alan Bradley. I liked this a lot when it came out, and apparently a bunch of other people did too, because it won four “Best First Novel” awards and a Dilys award, and was also a finalist for an Anthony for Best Mystery. Whew! The rest of the series is enjoyable too, IMO, and titles do go on sale occasionally, so if you read this one and like it, you’ll have found yourself a new series!
A year-and-a-half later, The Sweetness at the Bottom of the Pie is $1.99 again at Kindle US. It doesn’t seem to be on sale this time at Kobo US, at least as of now. The links in the OP are still good…