Combine pecans, sweetener, butter and cocoa in bowl of heavy-duty food processor.
Process until pecans are chopped finely and all are combined (will be somewhat wet).
Press mixture into bottom of 10" deep dish pie pan (using plastic wrap to cover nut mixture will keep it from sticking to your fingers and aid in spreading the nuts evenly). Set aside.
In bowl of same food processor (no need to clean bowl) combine cream cheese, cream, sweetener, coffee crystals, vanilla and 1 egg. Process until well blended, scraping down bowl. Add the next two eggs one at a time, scraping down the bowl between each addition.
Combined 4 T. butter and 8 oz chocolate in large microwave-safe bowl. Heat in microwave at medium power until melted.
Add melted butter and chocolate to mixture already in food processor; process for one minute.
Pour mixture from food processor into pie pan, spreading evenly.
Bake in preheated oven for 1 hour, checking carefully after 50 minutes. Do not allow top to burn.
Mix 2 T. of artificial sweetener with melted 1 ounce of chocolate.
Stir 1 T. of artificial sweetener into sour cream and vanilla.
Spread sour cream mixture over cheesecake, drizzling melted chocolate over in a swirled pattern.