Prepare the cake mix per the instructions on the package in a 9 x 13 inch cake pan. Bake per the package instructions.
Remove from the oven when it tests done. Immediately take a fork and poke holes over the hot cake.
Warm the hot fudge just enough to make it pourable then whisk together with the sweetened condensed milk.
Spread over the hot cake, into the holes.
Arrange the marshmallows on top and sprinkle 1/3 cup of mini chocolate chips over the marshmallows.
Return to the oven for 5 minutes to allow the marshmallows to melt and become slightly golden.
Melt the remaining 1 cup of mini chocolate chips in the microwave with 1/2 cup of heavy cream. Heat in 20 second increments stopping to stir each time. Repeat until smooth.
Drizzle over the warm marshmallows and crumble the toasted almond slices on top.
Allow to rest for 45 minutes.
Serve warm with vanilla ice cream or whipped cream if desired.