Q Can I bake challahs for my Shavuos milchig meal in a fleishig oven?
A Ideally, you should kasher the oven with a libun kal—by turning it on to 500°F (260°C) for one hour before baking the challah. Be sure to clean the oven thoroughly before kashering.
B’dieved, if the challah has already been baked in a fleishig oven (provided it wasn’t baked directly on a fleishig pan and the oven did not have actual meat residue), the challah can still be used for the milchig meal.