Prepare the pan and oven: Preheat the oven to 325°F (165°C). Thoroughly grease a 10- to 12-cup Bundt pan with 1 tablespoon (14 g) softened butter, working it into all grooves. Dust with 1 tablespoon (6 g) cocoa powder and tap out the excess.

Bloom the cocoa: Place the 3/4 cup (75 g) cocoa powder in a heatproof bowl. Gradually whisk in the hot coffee until smooth and glossy. Set aside for about 10 minutes so it cools slightly.

Combine the dry ingredients: In a medium bowl, whisk together the flour, baking powder, baking soda, and salt until evenly distributed.

Cream the butter and sugar: Beat the 1 cup (226 g) softened butter and granulated sugar on medium speed for 3 to 4 minutes. The mixture should look noticeably lighter and fluffy rather than dense or greasy.

Add the eggs gradually: Beat in the eggs one at a time, mixing for about 20 seconds after each addition. Scrape the sides and bottom of the bowl as needed. The mixture may look slightly curdled after the final egg but should become smooth once the remaining ingredients are added.

Add the vanilla and cocoa mixture: Beat in the vanilla. Add the cooled cocoa-coffee mixture and mix on low speed until the batter is evenly dark chocolate-colored.

Add the sour cream and flour in stages: Add one-third of the flour mixture and mix on low just until incorporated. Add half of the sour cream, followed by another third of the flour, the remaining sour cream, and finally the remaining flour.

Finish the batter gently: Fold the batter by hand with a flexible spatula just until no dry streaks remain. The batter should be thick, smooth, and spoonable. Avoid prolonged mixing once the flour is incorporated.

Fill the Bundt pan: Spoon the batter evenly into the prepared pan. Smooth the surface and gently tap the pan once or twice on the counter to settle large air pockets.

Bake the cake: Bake on the center rack for 65 to 75 minutes. Begin checking at 60 minutes. The cake should look set and slightly pulled away from the edges of the pan.

Check for doneness: Insert a long wooden skewer into the thickest section of the cake. It should come out with a few moist crumbs but no liquid batter. An instant-read thermometer inserted into the center should register approximately 205°F to 210°F (96°C to 99°C).

Cool briefly in the pan: Place the Bundt pan on a wire rack and let the cake cool for 15 minutes. Do not leave it in the pan much longer, as the cooling sugars can make the cake more likely to stick.

Turn out the cake: Run a thin flexible spatula gently around any accessible edges. Place the wire rack over the pan, invert both together, and carefully lift away the pan.

Cool completely: Let the cake cool on the rack for at least 1 hour 45 minutes. The exterior will firm slightly while the interior finishes setting.

Finish and serve: Dust the completely cooled cake with the optional powdered sugar. Slice into approximately 16 portions and serve at room temperature.