Preheat the oven to 425°. Microwave the butter and chocolate together for 1 minute. Whisk until mixed well and completely smooth.
Whisk in eggs and egg yolks until smooth. Whisk in vanilla extract. Whisk in the flour until smooth.
Divide batter among 4 greased ramekins (I used baking spray, you can also butter).
Place the 4 cups on a baking sheet and bake for 13 minutes. Sides will be firm and separating from the edges of the bowl.
Remove from the oven and let sit for 1 minute. Then using an oven mitt to hold the ramekin in one and and a plate in the other, one at a time, place the plate over the ramekin to flip and invert the cake onto the plate.
Serve right away with vanilla ice cream!
