Combine the cookie crumbs, butter and sugar in a bowl and stir until the crumbs are covered in the melted butter evenly. Pat the mixture firmly into the bottom and up the sides of a 9-inch pie pan.
Bake for 8-9 minutes, until the crust is firm. Remove and cool.
In a saucepan, mix sugar, cocoa, cornstarch and salt, then gradually whisk in the milk.
Cook, stirring frequently, over medium-high heat until thickened and bubbly.
Reduce heat; cook for 2 minutes more, stirring all the while. Remove from heat.
Temper the egg yolks by stirring in about 3 tbsp of the hot filling into the egg yolks.
Return to the saucepan and bring to a gentle boil, stirring continuously until it thickens up some more.
Cook and stir for another 3 minutes then remove.
Stir in the vanilla. Pour the hot filling into the pie crust.
For the meringue, immediately beat the egg whites with cream of tartar until soft peaks form. Gradually add the white sugar and continue to beat until the egg whites are stiff and glossy. Spread evenly over the hot pie filling, sealing the egg white meringue to the cookie pie crust. Bake at 350° for 12-15 minutes or until golden.