Cooking flan on the stove is an excellent alternative if you want to use something other than your oven. To do this, you'll need a large pot and a trivet. Place the trivet inside the pot and then put the pan with the custard on top of the trivet. Fill the pot halfway up the round pan with water and cook covered on medium-low heat for 50 to 60 minutes. Be sure to monitor the water level and add more if necessary. Also, cover the baking pan with aluminum foil to prevent water from getting into the custard.