TO MAKE THE CHOCOLATE SAND:

1. Preheat oven to 325 degrees.  
2. In a stand mixer fitted with the paddle attachment, beat the butter and sugar on medium-high speed until light and fluffy, 3 to 4 minutes. 
3. Reduced the speed to low and add the vanilla. 
4. In a medium bowl, whisk together the flour and cocoa powder. 
5. With the mixer running on low speed, add the flour mixture in three separate increments, including the cocoa nibs and salt with the final addition. 
6. Mix until the dough comes together.  (This dough can be refrigerated for a week or frozen for up to 2 months.)
7. Line a cookie sheet with parchment paper and press the dough into the pan in a 1/4 -inch thick layer.  This dough is very dense and may be difficult to spread.  Sandwich the semi-pressed dough in between two layers of parchment paper and use a rolling pin to press it out. 
8. Bake at 325 degrees F. for 8 minutes. 
9. Remove pan from oven and rake the semi-cooked dough with a fork to break into medium clumps.
10. Return to oven and bake for 7 minutes more. 
11. Rake cookie crumbles again to create smaller pieces. 
12. The streusel will look sandy and will crisp as it cools.