Preheat the oven to 350°F/180°C. Grease a 12-section mini muffin pan.
Put the butter in a small saucepan. Gently heat, uncovered, until it has melted. Take the saucepan off the heat and stir in the peanut butter, then the cracker crumbs. Divide among the sections of the prepared pan. Press it firmly over the bottom and sides of the pan with the back of a teaspoon.
Bake in the preheated oven for 6 minutes, or until slightly darker in color. Reshape the center, if needed, with the back of a spoon. Let stand to cool and harden in the pan for 10–15 minutes.
Meanwhile, put the chocolate in a heatproof bowl, set the bowl over a saucepan of gently simmering water, and heat until melted. Add the sugar and gradually stir in the cream until smooth. Preheat the broiler to medium.
Spoon the filling into the shells. Sprinkle the mini marshmallows over the top and press them lightly into the chocolate so they don’t roll off.
Broil for 3–4 minutes, or until the marshmallows have softened and are just beginning to color. Let stand to cool in the pan for 30 minutes, then loosen with a round-blade knife and carefully lift out of the pan. Serve.
This recipe is excerpted with permission from <a href="http://www.amazon.com/gp/product/1445444461/ref=as_li_qf_sp_asin_il_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=1445444461&linkCode=as2&tag=craftfocom-20">"Mini Pies: Gorgeous Little Pies and Tartlets,"</a> published by Parragon Books.