In a saute pan or small pot, combine 1 ¼ cup of milk, chocolate, salt and cocoa. Whisk over med-low heat until smooth (do not simmer).
Remove chocolate mixture from heat, pour into a small bowl or glass measuring cup, place in freezer and chill for at least 3 minutes, and up until overnight.
When ready to assemble the Frozen Hot Chocolate, rim your glasses in the marshmallow fluff and dip into the chocolate jimmies or shavings (if you choose). I do this by spreading some fluff on a plate and rolling the rim of the glasses onto it, then pouring jimmies onto a small plate and doing the same. It's just fun!
Place ice in your blender, add an additional cup of milk, add chocolate mixture and blend until ice is mostly crushed (you only want small splinters of ice).
Pour into your prepared glasses, add a dollop of whipped cream and enjoy!!
Notes
You can make your chocolate mixture and cool it in your freezer for 30 minutes, however, I personally enjoy allowing the mixture to freeze. Then scraping it onto the blender. This gives the Frozen Hot Chocolate a thicker consistency. If you do allow it to freeze, submerge your glass measuring cup or bowl in some warmish water to allow the mixture to release. I use a butter knife or spoon to "pop" it out and into the blender.Trick this delicious drink out any way you desire.Best made with whole milk.