Source: https://fcain.tripod.com/recipes/lemon_pie.html

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Ingredients
    One "tube" of frozen lemonade mix, thawed
    One can of sweetened, condensed milk
    One 8-oz. tub of Cool-Whip, thawed
    One graham cracker pie crust 

Equipment
    Can opener (the kind that punches a hole; not the kind that cuts off the entire top of the can!)
    Measuring cup
    Large mixing bowl
    Wire whisk       (optional)
    Spatula 

Instructions
    Thaw the lemonade and the Cool-Whip. You may thaw the lemonade on your kitchen counter, but you must keep the Cool-Whip in the refrigerator!
    After opening the "tube" of lemonade, measure out one cup of the lemonade concetrate (by using the measuring cup) into the large mixing bowl, and discard any leftover concentrate.
        Note: If the lemonade still has any ice crystals, stir the lemonade with the wire whisk until these crystals have dissolved. 
    Using the hole-punching kind of can opener, make a hole in the top of the can of sweetened, condensed milk. Then, make another hole in the top of this can such that if the first hole were "12 o'clock", then the second hold would be "6 o'clock". You may need to use the can opener more than once to make these holes large enough.
    Pour the milk into the mixing bowl. Mix well.
    Using the spatula, scoop the Cool-Whip out of the tub and put it into the mixing bowl.
        Note: If your tub of Cool-Whip is of the 12-ounce or 16-ounce kind, spoon out only eight ounces of the Cool-Whip. Eight ounces is half of the 16-ounce tub, or two-thirds of the 12-ounce tub. 
    Using the spatula, gently fold the Cool-Whip into the lemonade-milk mixture.
    Remove the plastic cover from the pie crust. Pour the blended mixture into the pie crust, but be careful not to overfill the pie crust. Discard any surplus mixture left in the bowl.
    Refrigerate the pie overnight. Promptly store any leftovers in the refrigerator.
 

Variation: Strawberry Cream Pie
    Instead of the "tube" of frozen lemonade concentrate, use a "tube" of frozen daiquiri mix. 

Variation: Lime Pie
    Instead of the "tube" of frozen lemonade concentrate, use a "tube" of frozen margarita mix.