My grandma always used to make thimble cookies that end up tasting a very specific way, before her passing she gave me the recipe so here it is if anyone else wants to try them.
Method (original): cream butter, add sugar gradually and mix well. Add well beaten egg yolk, flavouring and flour. Shape into balls about the size of a walnut. Dip in unbeaten egg white then roll in finely chopped nuts. Dent in centre with a thimble. Place on greased baking sheet and bake in moderate oven 350 F for 5 minutes. Dent them again. Bake 12~15 minutes. Fill with jelly while hot.
Method (my modified preference): cream butter, add sugar gradually and mix well. Add well beaten egg yolk, flavouring and flour. Shape into balls about the size of a walnut. Dent in centre with a thimble and brush on egg white. Insert the jam filling in each cookie. Place on greased baking sheet and bake in moderate oven 350 F for 15 ~ 20 minutes and promptly remove and place on cooling rack. If you leave the cookies to cool off in the tray they will over-bake as they're very temperature sensitive.
What I generally do is get raspberries and then boil them down (adding only a little bit of sugar so that the raspberries still have a bit of tartness), and then use that for the jam. With berries you don't need to add gelatin or pectin since they'll gellify on their own without it; gelatin is pretty gross anyways and I'm not certain why most people don't know berries can be naturally turned into jam without fillers.
For butter it's best if you get a more rich "old fashioned" style butter.
The nuts can be excluded (and probably should be anyways as more and more people have nut allergies these days).
And as a bonus here's a recipe for a rhubarb cake. My grandma once made a rhubarb cake since the old house had rhubarb that was planted and just kept growing of its own accord. My cat actually liked that rhubarb plant for whatever reason.
The wild cat in its rhubarb habitat
Well... it must have been unusual since it's uncommon to make cakes with straight up rhubarb and nothing else (the convention is generally rhubarb-strawberry with loads of sugar added which I think is disgusting). Anyways... grandma said she didn't quite remember doing that but provided this recipe for something equivalent, I guess?
The one she made didn't have coconut it was just cake crumble and the rhubarb WASN'T finely chopped, the pieces were actually larger and that's what made it great since you'd bite into a rhubarb chunk that had pockets of tanginess. I've yet to try the below recipe-- but if you're like me and only like rhubarb in things and NOT rhubarb-strawberry, then this might be something to attempt: