According to Quran you should always avoid matters of doubt. If you are cent % sure that all Alcohol evaporates then its safe and halal. if it doesn't evaporate you may try to make it evaporate by little warming, or whatever technique you find best. But make sure it is halal after that, you may use blue litmus paper, if it turns red (even the slightest shade of red) then alcohol is present, else not.
if the cake is dry then litmus paper won't change color. you should take a small piece from the cake after drying it and do the test. Best of luck
Remember necessity is the mother of invention/innovation