Preheat oven to 350 degrees (F). Heavily grease a 12-cup Bundt cake pan, then dust it with cocoa powder. Set aside.

Place 2 ounces of chopped bittersweet chocolate into a small heatproof bowl, and pour the boiling water over the chocolate. Whisk until smooth. Set aside to cool to room temperature.

In a large bowl, whisk together the cocoa powder, flour, pecans, confectioners' sugar, and salt.

In a small bowl, beat the eggs and vanilla together.

Using an electric mixer on medium-high speed, beat the granulated sugar, brown sugar, and butter together until light and fluffy. Reduce the mixer to low, add the egg mixture and beat until combined. Add the chocolate mixture and beat until thoroughly incorporated. Batter may appear curdled but that is normal. Mix in the flour mixture and beat until just combined. Don't over mix.

Pour the batter into the Bundt cake pan. Bake for about 45 to 50 minutes, until the edges slightly pull away from the pan and the top springs back when lightly touched. A skewer won't give an accurate measurement of doneness, so don't use.

Remove the cake from the oven and place on a wire rack. Cool in the pan for 1-1/2 hours, then invert onto a serving plate and cool completely.

Once the cake is completely cooled, heat the cream, corn syrup, and chopped chocolate in a small saucepan over medium heat. Stir constantly until smooth, then stir in the vanilla.

Remove from heat and allow to thicken for about 30 minutes.

Drizzle glaze over the cake. Add garnish if desired. Allow it to set for about 20 minutes before serving.