http://www.hillbillyhousewife.com/magicmilkshakes.htm Here is a link to the recipe listed below. Check it out to see her reasoning for the oil and spray. I'm giving it a try tomorrow.
Magic Milk Shakes
1/2 to 2 cups ice water
1-1/2 cups nonfat dry milk powder
2/3 cup sugar
1/4 cup unsweetened cocoa
1 teaspoon vanilla
1 to 1-1/2 trays of ice cubes, as much as you can spare
2 tablespoons corn oil plus a 5-second squirt of non-stick spray for emulsification purposes
Place all of the ingredients into the blender, including the oil and the non-stick spray. Use less water for thicker milk shakes and more water for shakes that are easy on your blender motor. The blender should be about 3/4’s full. Place the lid on. Process for a full 2 minutes. Pour into cups and serve. Makes 4 - 12oz servings.