I think the best plan is to break this one item into two recipes: the cookie, and the chocolate coating. The cookie is straightforward; just find a plain shortbread or butter cookie recipe, cut them into squares, and bake. By itself, the chocolate coating is also simple. I've had those cookies, and the chocolate coating is hard, not soft like ganache or frosting. So, all you have to do is buy a bar of eating chocolate and gently melt it in a double broiler (theKitchn has instructions for this somewhere). Once the chocolate has melted, spread it over your cookies. Wait for them to cool on the counter (or stick them in the fridge to hurry them up). And voila! Choco-Leibniz!

I love to dip cookies in chocolate, so I have quite a few! None of them are quite as simple as you describe, but you could always leave flavorings out.

Chocolate-dipped cinnamon malt cookies
http://outoftheordinaryfood.com/2012/10/17/chocolate-dipped-cinnamon-malt-cookies/

Chocolate dipped lemon pine nut cookies
http://outoftheordinaryfood.com/2012/08/21/lemon-pine-nut-chocolate-covered-cookies/

And chocolate dipped red wine cookies!!
http://outoftheordinaryfood.com/2012/06/15/red-wine-and-dark-chocolate-cookies/

I have a few other, but you said no chocolate cookies, right?

You want a "petit beurre", non a cookie, isn't? I found this in french, but the recipe is easy to understand:
http://pucebleue-jenreprendraibienunbout.blogspot.fr/2008/01/petits-beurre-maison.html

Looks like another blogger did just what you're asking for: http://andcute.com/leibniz-double-choc-copy-cat-cookies/

Bah! wrong recipe! http://journalofafrenchfoodie.com/tag/home-made-petits-beurre/

Hi AT!
Thanks for posting my question! And even more, thank you Katy did., Claireooto, mardete and keltrue for your help. This is so cool. The petit beurre looks like the way to go.

Best,
Jasmine