Preheat the oven to 425 degrees.
Coat 4 - 6 oz ramekins with butter. Dust with cocoa powder and shake to spread it evenly.
Place butter and chocolate into a medium microwave safe bowl. Microwave for 1 minute, until butter is melted.
Stir until chocolate is completely melted and mixed in with butter smoothly.
Whisk together the powdered sugar and flour in a small bowl. Set aside.
Whisk the eggs and egg yolks together in a small bowl.
Pour the flour mixture, egg mixture, and vanilla extract into the chocolate mixture.
Slowly stir together until its all combined. (The batter will be thick)
Spoon batter evenly into the 4 prepared ramekins.
Bake on a baking sheet and bake in the preheated oven for 12-14, until the top is solid, but you can see the middle is still wiggly.
Remove from oven and allow to cool for 1 minute.
Loosen sides with a knife.
Cover with an inverted plate and carefully flip over. (Use an oven mitt, they're still hot!)
Add ice cream, whipped cream, fresh fruit, or chocolate syrup. Serve immediately.