Start by coating the insides of your ramekins with cooking spray. Dust them lightly with granulated sugar, turning to coat evenly.
In a microwave-safe bowl, combine the chopped semi-sweet chocolate and unsalted butter. Microwave in 20-second intervals, stirring in between, until melted and smooth. If you’re using espresso powder, mix it in at this stage.
In a separate bowl, whisk together the large eggs, egg yolks, and powdered sugar until well combined and slightly frothy.
Pour the melted chocolate mixture into the egg mixture. Add a pinch of salt and vanilla extract. Gently fold until just combined.
Sift in the flour and fold gently until incorporated. The batter should be smooth and glossy.
Divide the batter evenly among the prepared ramekins. Leave a little space at the top for the cakes to rise.
Add 1 cup of water to the Instant Pot. Place the trivet inside and arrange the ramekins on top.
Close the lid of the Instant Pot and set the valve to sealing. Cook on high pressure for 10 minutes. Allow for a natural release for 5 minutes, then quick release any remaining pressure.
Carefully remove the ramekins from the Instant Pot. Let them cool for a minute, then run a knife around the edges to loosen the cakes. Invert onto a plate and serve immediately.