Line a large cookie sheet with parchment paper and set aside.
Gently break the full sheets of graham crackers in half to get 24 squares.
Generously spread the vanilla marshmallow frosting on one half of 12 of the graham crackers (I use the whole container in this recipe, but scale down if you like less frosting). Gently press the other graham cracker on top and smooth the edges with a knife so frosting isn't coming out the sides.
In a large microwave safe bowl, add in the chocolate chips and shortening. Place in the microwave and microwave in bursts of 15 seconds, stirring in between for 10-15 seconds (chocolate is melting even when outside of the microwave so it's important to be patient here) until melted.
Once the chocolate is melted and smooth, use a large fork to hold the sandwich cookie over the chocolate and a spoon, to spoon the melted chocolate over the sandwich cookie.
Gently tap the fork holding the sandwich cookie on the side of the bowl to remove excess chocolate. Transfer to the prepared cookie sheet and allow to sit until chocolate is hardened again (place in the fridge for a quicker set up!)
If needed, re-melt the chocolate in the microwave for 10-15 seconds in between dipping if it is getting difficult to dip.