Wash the lentils in a mesh strainer under cold water until the water turns clear. Set aside.
Mix the lentils with 1 qt. of water in a storage container. Soak for 6 hours at room temperature.
Drain the lentils in a mesh strainer and rinse with cold water to remove starchy residue.
Pulse purée the lentil mixture in a vitamix blender or equivalent.
Create a smooth, thick batter by streaming in cold water (about 10 oz.) with the blender on high.
Scrape down the sides of the blender to fully purée and remove lumps.
Whisk together the lentil purée and sifted rice flour in a large stainless steel bowl.
Add the remaining water (14 oz.) and whisk until smooth.
Ferment the mixture by placing it in a non-reactive storage container about twice the volume of the batter. Cover with plastic wrap and let it rest at room temperature overnight. NOTE: The batter isn’t ready until there are noticeable air bubbles throughout the batter. This could take two days (or warmer air temperature).
Refrigerate the fermented batter until needed for service.