To loosen flans, creme caramel or other custards from their ramekins, you can run a knife around the inner edge, but this runs the risk of dinging the caramel so it'll be scarred once unmolded-that's not the most appealing dessert. But you can get your custards out of their molds in one piece, because there's a better way.
This tip works on flans, creme caramel, and most other types of firm custards: Instead of loosening custards with a knife, hold the ramekin upright but slightly tilted, and then give the side of the ramekin a good whack with the heel of your hand-this will break the vacuum between the custard and the ramekin.
Now immediately turn upside down onto the serving plate-if you set it down and wait to unmold, the vacuum may re-form. Give the ramekin and plate a few firm shakes together-you'll hear a slurp as the custard slides onto the plate.