You don't finish cooking your steak in the oven.
Popping your steak in the oven after you've seared and basted it will ensure you get an even cook. Place your steak in an oven preheated at 450°F (230°C) and bake it for 7 minutes for medium-rare. (That timing is for a sirloin cut, so make sure to adapt it depending on the thickness of your steak).