Betty Crocker came out with a Hershey's S'mores cupcake mix where you bake the marshmallow filling right in the cupcake instead of filling the cupcake after it's baked. I would like to try my own version of this but can't find a marshmallow filling that you can bake right inside the cupcake batter. Can anyone help me out with this?

Thanks!

I'd also be interested in other bake-able filling recipes that people have tried and know are good.