To make soft-serve ice cream at home without an ice cream machine, you need 35 ounces of whole milk, 3.5 ounces of heavy cream, 8 ounces of sugar, a dash of salt and 3.5 ounces of nonfat dry milk powder. The process also requires 1/2 ounce of pure vanilla extract, dry ice, a blender, a stand mixer and a disposable piping bag.
To make the base, mix the whole milk, heavy cream, sugar, salt, vanilla extract and milk powder in a blender for about one minute. Cover the mixture, and place it in the freezer. For maximum smoothness, heat the mixture to 175 degrees Fahrenheit to dissolve the milk proteins and prevent grains and chunks in the finished product. Chill the mixture thoroughly before churning it.
Place the dry ice into a bag or wrap it up in a bath towel, and crush it into a fine powder with a cast-iron pan or a hammer. Transfer the crushed ice into a plastic bowl or Tupperware. Pour the ice cream base into the bowl of a stand mixer, and begin mixing on low using the paddle attachment. Add dry ice one spoonful at a time, and allow foam and steam to dissipate before adding another spoonful. Once the ice cream begins to thicken, increase the mixing speed, and continue to add spoonfuls of dry ice until the mixture reaches the appropriate consistency. Store the ice cream in a piping bag in the freezer until ready to serve.