The custard can be prepared on the cook-top or in the oven. First you add sugar and water to the pan and swirl over a hot burner to melt the sugar and form the caramel. The pan is then filled with the custard mixture and placed over a pot of boiling water (either in an oven or over a double boiler) where it remains until the custard is set, about 1 hour.
The custard is cooled, then inverted on a plate. The flan is cut in wedges and served with the caramel poured over the top.