Preheat oven to 450°F. Rub butter all over the inside of two 6 oz ramekins and then swirl around cocoa powder so it covers the inside. Knock the excess cocoa powder out.
Put butter and chocolate into a glass bowl and microwave in 30 second intervals, mixing in between, until it's fully melted. Whisk in sugar and salt. Then add the egg and egg yolk and whisk thoroughly about 20 times until the mixture looks smooth and glossy. Lastly, mix in the cocoa powder.
Pour in equal portions into the two ramekins. Cook for 7-9 minutes depending on your oven or how gooey you want your center to be.
Serve with whipped cream and eat immediately.