Grease bottom and sides of a 9-inch springform pan with butter. Line the bottom with parchment paper, spray with non-stick spray, then dust the paper with cocoa powder.

In a microwavable bowl, combine the bittersweet chocolate, 4 oz. of semisweet chocolate, and 3/4 cup of the butter. Microwave on MEDIUM until melted and smooth, about 2–3 minutes, stirring after 1 minute and then every 30 seconds. Stir to glossy perfection and let cool for 15 minutes.

Preheat oven to 300°F (about 150°C).

In a large bowl, beat the eggs, sugar, coffee, salt, and 2 tsp. vanilla with a stand mixer on medium-high speed until very foamy and pale, about 3–4 minutes.

Gradually add the cooled melted chocolate mixture to the egg foam. Beat until well blended and even in color.

Sift the 1/4 cup cocoa over the batter; beat on medium-low speed until combined, about 30 seconds.

Pour batter into the prepared pan and bake for 40–45 minutes, or until a thermometer reads 140°F in the center.

Cool in the pan on a wire rack for 30 minutes. Gently push down the cake edges until even, run a knife around the sides, and remove the springform sides. Flip the cake over onto a cake plate, remove the bottom and parchment paper. Cool 1 hour, then cover with plastic wrap and chill for 8 hours or overnight.

In a microwavable bowl, add the 4 tsp. corn syrup (or honey), remaining 6 oz. semisweet chocolate, and remaining 1/4 cup butter. Microwave on MEDIUM until melted, about 1–1.5 minutes, stirring every 30 seconds.

Stir in remaining 1/2 tsp. vanilla.

Pour glaze over the chilled cake, spreading to coat top and sides. Press toasted pecans into the sides.

Chill cake 20 minutes before serving.