In the bottom of a cold crockpot, whisk sweetened condensed milk with cocoa powder and vanilla until smooth.
Whisk in milk, half & half and creamer, being sure to get to the edges. Sprinkle in the salt. Cover and warm on high for 2 hours or low for 4. You're not trying to cook this, just warm it through! Once it's to the desired temperature, switch crockpot to 'warm'.
When you're ready to serve, add in mini marshmallows and more coffee creamer if you so desire {which you totally should!!} Enjoy!