there’s many ways to make one. it’s just a shortbread crust with jam . . .
so it depends on how close to ‘authentic’ (EGAD!! that again!!) you wish to stick.
pecans are not native to Europe - so that would rule them out
imho, it ain’t right without floured almonds in the AP - 2 parts AP, 1 part almonds by weight.
the nuts need to be cooked, not raw. I do a light toasting - as in near-no color toasting - keep a nose out for the aroma release . . . shortly after that, they’re ready.
I have used hazelnuts - works fine, but almonds are my personal preference.
the jam . . . Europe has a number of “berries” which are not commonly available in USA - once again the ‘authentic’ issue . . .
my preference is (seedless) blackberry jam/preserves, although raspberry is likely closer to those ‘authentic’ made in Linz (company has a factory there, gained a couple pounds every trip…)