Graham crackers have not made it to the UK yet, so of course s'mores don't exist here either. They are one of those things I did not eat often in the states, however as soon as I can't have them...
One of my class mates brought over these soft graham cookies last summer and they were delicious! I hadn't realized that baking a cookie with the flavor of graham crackers was soo easy (homemade graham crackers just didn't seem worth the effort). These cookies are definitely worth making and eating on their own - but of course I figured they might be improved by adding in chocolate and marshmallows.
I tried a few variations of stuffed cookies, then found that a bar cookie was less effort, and allowed a better distribution of chocolate and marshmallows in every bite. Luckily none of my friends complained at having to try 4 or 5 variations of these cookies over the last few weeks... I used milk chocolate in my last edition, to make it more similar to the S'mores of our childhood - but they are also delicious with a dark chocolate, if you want a more adult version.