Preheat the oven to 350°F. Arrange the mini pie crusts in a rimmed baking sheet.
Make the brownie mix according to the package directions: Stir together the mix, oil, water, eggs, and a pinch of salt in a large bowl with a spatula, wooden spoon, or hand mixer until smooth.
Divide the batter evenly between the pie crusts. Bake for 20 minutes or until the brownies are set. (If you insert a toothpick in the center, the toothpick will not come out clean.)
Remove the pies from the oven and let cool until warm or to room temperature. Dollop a little marshmallow cream in the centers of the pies. Use a kitchen torch or the broiler to toast the marshmallow.
Let the marshmallow cool slightly. Break the chocolate bar along the grooves and place one small rectangle (there will be 12) in the center of each pie to garnish, if desired. Serve warm or at room temperature.