It's slightly crusty on the outside, and the middle of the cupcake, still finishing baking in its own heat, is gooey. (inc.com)
You can use a cupcake plunger, or take a sharp knife and cut out a cone shape from the middle of the cupcake (you don't NEED to put these bits back on after you fill the cupcakes, so feel free to eat them as you go!). (shakebakeandparty.com)