Serves 12 

1 15.25-ounce box devil’s food chocolate cake mix
1 - 7-ounce container marshmallow creme, slightly melted
1 - 14-ounce can sweetened condensed milk
6 full-size graham cracker sheets, coarsely chopped into 1/2-inch pieces
1 to 1 1/2 cups mini marshmallows
1/2 cup hot fudge, for drizzling (store-bought or homemade)

Preheat oven to 350F. Spray a 9×13-inch pan with cooking spray; set aside.
Make cake according to package directions (likely adding 3 eggs, water, and oil) and bake as directed (likely about 25 to 30 minutes).
While the cake bakes, remove the seal from the marshmallow creme, and heat it for about 10 to 15 seconds on high power in the microwave, just enough to soften it. Watch very closely because it will puff up very quickly and you don’t want it to overflow.
Using a spatula, scrape the marshmallow creme into a large bowl.
Add the sweetened condensed milk and whisk to combine; set aside.
Remove cake from the oven when it’s done and using the blunt end of a wooden spoon, poke holes over the surface of the cake. I didn’t count but I estimate I poked about 60 holes, evenly spaced over the surface.
Slowly pour the marshmallow and sweetened condensed milk mixture over the holes, taking your time to evenly distribute it so that all the holes receive some.
Evenly sprinkle the graham crackers. Evenly sprinkle the marshmallows.
Lightly toast the marshmallows with a handheld torch. I haven’t tried using the broiler and cannot speak to the results or the duration. Likely less than 1 minute and if you try it, watch it the entire time and don’t turn your back on it for a second because it will be very prone to burning. Alternatively, omit toasting step if you’re not confident with your broiler.
Evenly drizzle with hot fudge before serving. Cake will keep airtight for up to 5 days noting the graham crackers soften and marshmallows become gooier over time.