Brew the espresso.
Add the egg yolks to the bowl and slowly pour in the sugar while mixing gradually with a hand mixer until foamy.
Gradually drizzle in espresso and Cognac, and keep mixing until combined.
Transfer the mixture to a saucepan over medium heat. Stir until it starts to simmer. Keep whisking until the egg yolks are cooked and the mixture begins to thicken and double in size. This should be within two minutes.
Remove from the heat once the custard feels like whipped cream. Keep whisking off the heat for one more minute.
Let the custard chill and store it in a mason jar, cover it with a lid, and place it in the freezer overnight.
Take the custard out of the freezer about ten minutes before serving. The custard should have begun to soften. Sprinkle with cocoa powder or powdered sugar on top and serve with a spoon.
