Heat the oven to 350°F. Grease a 9-inch springform pan and wrap the outside securely with heavy-duty foil if using a water bath.

Combine the chocolate cookie crumbs, melted butter, and optional sugar. Press the mixture firmly into the bottom of the pan, bake for 8 to 10 minutes, and cool slightly.

Reduce the oven temperature to 325°F. Beat the softened cream cheese and sugar on medium-low speed until smooth, taking care not to add excessive air.

Add the melted, slightly cooled chocolate, then mix in the sour cream, vanilla, and salt. Add the eggs one at a time, mixing only until each egg is incorporated.

Pour the filling over the crust. Place the springform pan in a larger roasting pan and add enough hot water to reach about halfway up the sides.

Bake for approximately 65 to 80 minutes, until the outer edge is set and the center still has a slight wobble. Turn off the oven, crack the door, and leave the cheesecake inside for about 30 minutes.

Remove the cheesecake from the water bath, cool it completely, and refrigerate for at least 6 hours or overnight.

For the topping, combine the evaporated milk, sugar, butter, and egg yolks in a saucepan. Cook over medium heat, stirring constantly, for 8 to 12 minutes until thickened without allowing the mixture to boil aggressively.

Remove the topping from the heat and stir in the vanilla, coconut, and pecans. Cool it until spreadable, then cover the chilled cheesecake and refrigerate until serving.