Mix egg, Dijon mustard and salt (skip if crab meat is salty). Add crab meat, celery, and rice flour into the mixture, stir to combine. Heat a skillet, spray some oil or butter on it. Drop about 2 tablespoon of crab mixture per cake into the skillet. Put as many as you can fit, leave some space for spatula to turn them. Press the cakes flat using the spatula. Let cook for 2 minute over medium heat. Flip over and cook the other side. When the cakes are no longer runny and a little brown on the edges, they are ready. Serve alone or with steamed vegetables.