Take 1 cup of roasted rice flour in a bowl and add the boiled water into it little by little and stir. Mix continuously till the dough is formed. Using your hands (be careful the dough can be very hot), knead together until you get a smooth and soft dough. The dough should not be too tight and it should not be sticky also.
Now take a noodle maker and fill in the dough. Grease the idli plate with oil and press the noodle maker in a circular motion. Fill in with grated coconut if you wish.
Once the water starts boiling in the steamer, place the idli molds and steam for 7-9 mins on medium-high flame. Keep the steamed closed for a min or two. Transfer the cooked Idiyappam to a serving plate.
Recipe by Kerala Cooking Recipes at https://www.keralacookingrecipes.com/idiappamnoolappamnoolputtu-rice-flour/