Line a baking sheet with parchment paper. Roll the pie crust flat on a lightly floured surface, dusting with flour as needed to prevent sticking. Use a 1 1/2- to 2-inch square cookie cutter to cut out 8 pieces (see Cook's Note). Gently transfer the squares to the lined baking sheet. Use the tines of a fork to dock several lines in each of the squares to prevent too much rising. Wrap the baking sheet in plastic wrap and refrigerate for 1 hour.
Preheat the oven to 400 degrees F.
Unwrap the baking sheet. Bake the pie crust squares until lightly golden brown, about 10 minutes. Cool on the baking sheet completely.
Preheat the broiler.
Cut each of the jumbo marshmallows in half horizontally to yield a total of 8 flat marshmallow pieces. Place a chocolate square on each of the pie crust squares, then a marshmallow half on top of each chocolate square. Put the s'mores under the broiler just long enough to brown the tops of the marshmallows, about 2 minutes. (Alternatively, use a kitchen torch to toast the outsides of the marshmallows.)
To prevent sticking, dip the cookie cutter and fork in flour occasionally and shake off the excess.