Preheat oven to 425°F. Grease four 5oz ramekins with butter and dust with cocoa powder. Gently tap ramekins to get rid of excess cocoa powder. This process will help the cakes slide gently out of the ramekins.
Place chocolate and butter in the top of a double boiler. Let cook until chocolate and butter are melted and fully combined. Alternately, you can place both chocolate and butter in a large microwavable bowl and cook on high, stirring every 10 seconds, until smooth and combined.
In a small bowl, sift together flour, powdered sugar, and salt. Set aside.
In a small dish, whisk together eggs and extra yolks.
With a rubber spatula, gently fold the flour and egg mixture into the chocolate. If there are any lumps, gently press them out. Be careful not to overmix. Batter should be a little thick.
Evenly distribute amongst the ramekins and bake for 12 minutes. If making in a muffin tin, bake for 10 minutes. Remove from oven and let sit in ramekins for 1 minute. Invert onto a plate and let sit for about 30s before gently removing ramekin. Serve with vanilla ice cream and chocolate port sauce.
