Melt the chocolate and butter together in a glass bowl in the microwave,at 30 second intervals. After 30 seconds, stop, mix and pop in again until all melted and combined.
In a large bowl add 2 large eggs, 2 large egg yolks, ¼ cup castor sugar, and a pinch of salt.
Slowly mix the melted butter into the egg and sugar mixture
Fold in flour and vanilla extract
Pour into buttered ramekin dishes
Add in one cup of water to your instant pot and place trivet stand inside. Place chocolate filled ramekin dishes inside (you should fit 3 at the bottom on at the top).
Close Lid and seal, set to high pressure for 8 minutes (I think I did 9 in the end) and quick pressure release.
Lift lid carefully off taking care not to spill condensation onto cakes.
You can either serve immediately or refrigerate until needed (and then warm up)
Dust with a little icing sugar and cocoa powder.