Preheat your oven to 180℃ fan (200℃ conventional)
Add butter and chocolate to a microwave-safe bowl and microwave for 30 - 45 seconds.
Once the butter is melted, mix until the chocolate is fully melted. Set aside to cool.
Coat two ramekins with butter and dust with cocoa powder, and set aside
Add the egg and sugar to a mixing bowl and with a hand mixer on medium speed whip them until fluffy (about 2-3 minutes)
Add the butter and chocolate mixture to the egg and sugar mixture, and using a spatula, fold together. (Avoid whisking or mixing)
Fold in the flour, cocoa powder and salt. (Avoid whisking or mixing)
Pour the mixture evenly into the two ramekins and bake for 15 minutes. (Until the edges are set, but the centre stays soft with a slight jiggle)
Once baked, remove the ramekins and leave to rest for at least 2-3 minutes
Use a butter knife to loosen the edges before turning it over onto a serving plate
Dust with Icing (powdered) sugar and serve straight away.