Crust: melt butter and stir in 1/4 cup sugar. Add crushed crackers and toss to mix well. Spread evenly into a 9-inch pie plate and press onto bottom and sides. Chill 1 hour or until firm. Can also bake in a 375 degree oven for 4-5 minutes and then cool before filling.
In a medium bowl, beat egg yolks with a whisk or a fork. gradually whisk/stir in condensed milk. Add lime juice, water, and a few drops of green food coloring if desired. Mixture will thicken as you stir.
Spoon filling into the crust. Bake in a 350 degree oven for 25 minutes and cool for 1 hour, then chill for 3-4 hours. Top with whipped cream and serve.