I would definitely want locally-or-homemade rhubarb jam; too many people seem to think rhubarb requires a bucketload of added sugar, which is the exact opposite of the point of my eating it. (I like tart things, okay! Please, world, stop adding a pound of sugar to everything even slightly acidic?) Someone else in the comments suggested redcurrant, and that would be excellent, too; they have excellent tartness and a beautiful colour!

I have never had an issue with shortbread recipes being tricky, but then, I use the most basic recipe in the world, and just adapt it as needed. (I must admit, I laughed hard at the recipe someone linked above; "easy" is not a descriptor I'd use for a recipe that requires a stand mixer, rolling out while chilled, and not one but two refrigeration stages!) The only time I've ever screwed up my shortbread was the first time I tried to make a chocolate version using cocoa; the darker dough made it hard to judge doneness and it got burnt around the edges before I pulled it out.

...Now I need to figure out a honey-ginger version, don't I. This will be tricky!