Lime and Avocado Pie

2 limes
1 avocado
1 egg yolk
1 can sweetened condensed milk
Whipping cream
Graham cracker pie crust

Mash avocado. Add egg yolk and sweetened condensed milk. Mix well. Add the juice from the 2 limes to the avocado mixture. Stir well; mixture will thicken as you stir. Pour into graham cracker pie crust. Top with whipped cream before serving. Chill for at least several hours before serving.