This is not a cake or cupcake, but it is something that says birthday to me. My grandpa used to make this for me for birthdays, he made them filled with apples, raisins, sugar and everything for everyone else but I didn't like those, so the chocolate filling was for me.
It's just puff pastry with some chocolate pieces inside it, if you want you can use some egg on top for a nice colour and sprinkle on some sugar before putting it in the oven.
Letting it cool down a bit might be wise, molten chocolate is hot (I know from experiencing it often…)