I've seen (or maybe heard) of people sticking chocolate or chocolate candies into cupcakes straight out of the oven. What kind of chocolate do they use? and does the chocolate harden when it cools down or does it stay gooey?
I've not done this AFTER they come out of the oven but I have put candy bar pieces or an oreo in the batter before it bakes. Your end result will depend on the candy you are using (some candy bars are softer than others after cooling) but I have found they all firm up after the cupcake cools to room temp. A chocolate lava cake is made using an altered recipe and is almost undercooked. This is what gives it the ooey gooey middle.