What is the best way to caramelize sugar for flan?

Don't over caramelize your sugar. The caramel needs to be a nice golden amber shade. Use a saucepan with a light colored interior so you can easily tell the color of the caramel. Let the saucepan do all of the work. While you’re making the caramel, swirl the saucepan to distribute the color, and avoid stirring. In a medium saucepan, combine the sugar and ¼ cup water and set over low heat. Increase the heat to medium and cook, occasionally swirling the pan to distribute the caramelized sugar—do not stir or the sugar will seize and crystalize—until the mixture is amber in color, 8 to 12 minutes.