Butter the ramekins and set them aside.
Add 1 cup of water to the instant pot and set the trivet inside.
In a medium mixing bowl, add butter and chocolate. Microwave in 15-second intervals, until the butter, is melted. Whisk well until the chocolate melts. The mixture should be smooth.
Add powdered sugar and espresso powder. The mixture should be thick and smooth.
Add egg and egg yolk and vanilla and whisk well.
Add flour and salt and fold in with a spatula. Do not overmix!
Divide the chocolate batter evenly among the ramekins. Place ramekins onto the trivet in the Instant Pot.
Close the lid and point the valve to the "sealing" position. Newer models do it on their own.
Cook on high pressure for 8 minutes.
When the timer is done, press the "cancel/off" button. Do a quick pressure release.
Carefully open the lid and wearing an oven mitt, remove ramekin from the IP.
Cover each ramekin with a plate, flip over, tap the ramekin and gently remove the cake.
Let it cool for a few minutes, dust with powdered sugar and serve.