Arrange 9 pretzels on a baking sheet. Cover each with three mini marshmallows. Broil until toasted.
Top each with a square of chocolate. Turn off the broiler and return the pan to the oven until the chocolate melts. Top each with another pretzel. Allow to harden (you can put it in the freezer if you’re in a rush).
Melt the chopped chocolate in the microwave, stirring every 30 seconds until smooth and thin enough to dip s’mores into. When the pretzels are firm enough, dunk each one in the chocolate using a fork. Tap the excess chocolate off, allowing it to return to the pan. Sprinkle with jimmies or other sprinkles if desired, and place s’more on waxed paper to set.