Mix sugar with egg in a small straight-sided bowl. Add milk and lemon flavoring. In another small bowl, mix flour, xanthan gum and salt. Slowly add dry ingredients to egg mixture and stir or whisk until smooth.
Heat 3 inches of oil to 375 degrees in a small saucepan. Heat rosette iron in oil. Remove and tap off excess fat on paper towel. Dip iron into batter until 2/3 covered (you don’t want batter to completely cover the iron). Immerse in hot oil. Fry until brown. Remove from oil, draining. Use a sharp fork to push rosette off the iron. Cool cookies either side up. When cool, sprinkle with confectioner’s sugar. Store in a wax paper-lined box. Best eaten within a day or two.