Brush your ramekins with butter or spray, then dust lightly with the cocoa powder. Place on a baking sheet and set aside.
Preheat your oven to 450 degrees.
Place the butter and chocolate in a microwave-safe bowl. Microwave in 30-second increments on 50% power. Stirring after each 30 seconds. Once the chocolate is almost all the way melted, remove and stir until it is all melted. Set aside.
Add eggs, egg yolk, and brown sugar to a bowl. Mix with a hand mixer until light and fluffy. Pour in the chocolate mixture and vanilla, mix to combine.
Divide the batter between the 4 ramekins. Drop 1-2 tablespoons peanut butter into the center of the mixture.
Move the baking sheet to the oven. Bake for 12 minutes. You want the outside to be slightly set and the center soft.
Remove from oven, and allow the cakes to sit for about 1 minute. Slide a knife around the edges to make sure the cakes will slide out easily. Invert carefully onto a plate and slide the ramekin off.
Dust with powdered sugar, if you choose. Then top with ice cream or whipped cream.
Serve immediately, as the molten cake will continue to cook and you won't have the gooey center.
Now, sit back and enjoy!
