Preheat oven to 350 degrees F.
Add chocolate and butter to a medium, microwave-safe bowl and microwave until melted. Stir until smooth, and add vanilla extract to the mixture.
Add sugar, cocoa powder and cornstarch to a small size saucepan and place it over medium heat.
Once sugar is melted, whisk in heavy cream and cook stirring until the mixture thickens and is bubbly, for about 5-8 minutes. Reduce heat to low and simmer for 2-3 minutes. Remove from heat and set aside.
Add room temperature egg yolks to a small bowl. Whisk in a small amount of the CREAM mixture into the egg yolks, continuing to add small amounts. You don't have to add ALL the mixture to the eggs, just enough to temper them, so they don't curd when combined with the hot mixture.
Add the EGG mixture to the remaining CREAM mixture and place the pan over medium heat. Whisk constantly and bring to a gentle boil, cook stirring for about 2 minutes. Remove from heat.
Stir in melted chocolate mixture until fully combined.
Fold in the chopped pecans.
Pour chocolate mixture into the prepared crust.
Bake for 25-30 minutes, until set.
Cool completely before adding the Coconut-Pecan Topping.