Any ingredients you've thought of, but have been unsure how to work into the recipe? Let's talk about it and help each other out!
What are you thinking it would bring to a stout? Nutty flavor? You might want to consider that tahini is more than 50% fat. Adding it would probably be detrimental to foam retention, if you care about that.
Tahini might be tough, because it contains so much fat it will absolutely kill head retention. You could try fat-washing it in liquor and then add the liquor. Basically, dissolve the tahini in liquor in a sealed container and shake the shit out of it daily for a few days, then let it all sit and settled for a day or so, freeze overnight, and then filter out the liquid and add that to the beer at packaging.
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I'd like to add that both Radical Brewing by Randy Mosher and Experimental Homebrewing by Drew Beechum and Denny Conn have good tips on how to use unorthodox ingredients.
Just my 2 cents... the higher the proof, the better the extraction. Everclear has always been a great solvent for extracts/tinctures
I'd be more interested in toasted sesame in a pale, clean lager-like beer. Stout might overpower that taste. But really what I want now is a burger on a toasted sesame bun with fries and a pilsner. Sometimes pairing food and beer in the traditional way is way more satisfying than flavored beers. And by sometimes, I mean just about always.
I'd say no tahini in beer; just toast a few sesame seeds and throw them in secondary, like 'dry beaning' with coffee.