I have never been particular successful making truly great s'mores. In particular, the chocolate never melts; I've always envisioned a sticky, luscious mix of melted chocolate and marshmallow squishing out between the graham crackers. But last night, I think I hit on the right approach (now obvious).
First, the marshmallow must be thoroughly melted and hot. This means a long roast time to get the inside as goopy as the outside. No flaming torches here. Lots of turning and patience here.
Once you have the completely soft marshmallow and assemble the s'more, you need to let the whole thing sit for a few minutes so the heat of the marshmallow can melt the chocolate. This is hard with eager kids, so in practice, I could only do this after handing a frankly half-done s'more to each kid. M-m-m.
I suppose you could this with chocolate sauce instead of a chocolate bar, but that seems like cheating and frankly un-American.
That said, I discovered that I like just marshmallow and graham cracker better than the normal way with chocolate. It's a lot less cloying and doesn't have any of that annoying waiting around.