Place half of the chocolate milk, half of the Nesquik powder, half of the sweetened condensed milk, half of the whipped topping, and half of the vanilla in a blender. (see note) Cover and blend until well mixed and combined.
Pour into a 9-inch x 13-inch baking dish. Place into the freezer.
Repeat with the remaining ingredients and pour into a second 9x13 baking dish.
Every 30 minutes, scrape and mix the frosty to break up the ice crystals. Focus on the outer edges, they freeze first. Keep doing this until it is frozen to your liking. I like my frosty more solid which takes about 6 hours in the freezer. If you like your frosty on the slushy side, it should be ready aaround 4 hours.
Notes
You have to blend this in two batches because all of the ingredients will not fit in a standard blender at one time. If you don’t have a blender, you can use a food processor or an immersion blender instead.
You can put the whole mix into a large bowl if you don’t want to add it to two separate 9x13 containers. This recipe does make a lot so it takes a while to freeze, this is why I suggest two containers to make the process as fast as possible.
The frosty mix does freeze nicely, but since it is more of an icy consistency it will start to melt faster than ice cream. If left in the freezer overnight, it will freeze almost solid, but it is still relatively easy to scoop some out and enjoy it.
If you don’t want to use whipped topping, freshly whipped cream will work as well. Whip ½ cup heavy whipping cream plus 2 tablespoons of powdered sugar to stiff peaks. Instead of adding the whipped cream to the blender, blend the chocolate milk, Nesquik, sweetened condensed milk, and vanilla together. Then pour the chocolate mixture into a large bowl and fold in the fresh whipped cream before freezing.