Mix the dough. In a bowl, combine flour, cornstarch, yeast, sugar, and salt. Slowly add warm water while mixing until you get a smooth, sticky batter.
Let it rise. Cover the bowl and let it rest in a warm place for about 1 hour until bubbly.
Prepare the syrup. In a saucepan, boil sugar and water together. Add lemon juice and simmer 10 minutes until slightly thick. Stir in rosewater if using. Cool completely.
Heat the oil. Pour oil into a deep pan, about 2 inches deep. Heat to 350°F (175°C).
Shape and fry. Scoop small spoonfuls of batter and drop them carefully into hot oil. Fry until golden brown, turning often.
Coat with syrup. Remove fritters with a slotted spoon, drain quickly, and toss in cooled syrup until well coated.
Serve hot. Eat right away for the best crunch.