Deep-fried batters and doughs account for some of the world's favorite sweet treats, from doughnuts and crullers to funnel cakes and churros. Rosette cookies provide an especially delicate example of the style, made by dipping a specially shaped iron into your batter and then into hot fat. The finished cookies slide easily from the iron, with a modest assist from you.
Check that your rosette iron is scrupulously clean before you start, because dried-on batter can cause the cookies to stick. Bring your oil up to a temperature of 325 to 350 degrees Fahrenheit, and rest your iron in the oil to preheat. Some sources suggest 10 to 15 seconds of preheating, but cookies are less likely to stick if you heat the iron for a full minute. Once it's ready, dip your iron into the batter. Take care not to let your batter come over the top of the iron, otherwise the cookie will not come off. Lift it out and let the excess batter drain for a moment, then place the batter-coated iron into the hot fat.
Fry each cookie until it's just golden-brown. Some will detach from your iron and float free in the oil, and some will remain on the iron. Both are perfectly normal. Carefully lift out floating cookies and transfer them to clean paper towels, hollow-side down, to drain. If the cookie sticks to your iron, gently sliding it with a fork or butter knife should release it. If you've dipped too deeply into the batter, and your cookie encases the iron, scrape the top of the iron with your fork to remove that portion of the cookie. The cookie should then detach easily.