Preheat oven to 350 degrees. In a medium bowl, stir together pecans, 3 tablespoons sugar, vanilla wafer crumbs, and cinnamon. Mix in melted butter. Press mixture onto bottom and up sides of a 9-inch pie pan. Bake for 8-10 minutes. Cool completely.
In a small bowl, Stir together espresso powder and boiling water until dissolved.
In a medium saucepan with a heavy bottom whisk together sugar and cocoa powder.
Whisk in whipping cream, corn syrup, and espresso mixture.
Add chopped chocolate and butter and bring to a boil over high heat, stirring constantly. Reduce heat to a simmer for about 4 minutes, stirring frequently. Remove from heat and stir in vanilla extract. Let cool for 45 minutes to 1 hour.
Remove 1 pint of ice cream from the freezer and let it get soft. Spread evenly on bottom of crust. Drizzle 3-4 tablespoons of sauce on top. Freeze for about 15 minutes and get the other pint out to soften.
Spread second pint evenly on top. Place back in freezer to freeze completely.
To serve, drizzle sauce on top and add whipped topping if desired.