Yes, you can. However, the oven method is much harder to control the temperature and how quickly the flan cooks since you are cooking it blindly. This may yield a lot of air bubbles in your flan. To cook the flan in the oven, preheat your oven to 350 F. Cover the ramekins with foil. Place the ramekins into a larger tray and place them in the middle rack in the oven. Pour in enough hot water into the tray so that it reaches about 1/2 way up the ramekin. Bake for 40-45 minutes or until the outer rim is set and the center has slight jiggle-like jello.