Sift 1 1/2 cups and 1 1/2 tablespoons rice flour into a bowl through a sieve. Add grated coconut and salt; stir to combine. Mix in warm water while stirring mixture with your fingers until it resembles small crumbs.
Transfer flour mixture to a pittu mold. Cook until steam appears from the vents on top of the mold, 8 to 10 minutes. Remove from heat. Let stand for 5 to 8 minutes before removing the pittu from the mold.