Combine 1 cup urad dal & 1/4 cup moong dal. Wash both lentils for couple of times. Soak dal in sufficient amo of water for 6-7 hours or overnight.

Transfer soaked dals into grinder jar & grind into smooth batter. I ground into two batches. Add little water while grinding & should have very smooth consistency like cake batter.

Transfer ground batter into wide bowl. Keep this batter into freeze for about one hour. After one hour whisk batter into one direction with whisker for about 10 minutes. or until it turns fluffy. Whisking incorporates air into the batter. Add water if required while whisking. As more you whisk the vada will be more spongy. Now batter is ready.

Add cumin seeds, curry leaves, & salt & green chili chopped into batter. Mix all ingredients well. Whisk again. Heat appe pan. Grease appe pan with oil. Pour batter into each cavity.

Cover appe pan with lid for about 3-4 min on low flame. After 4 min remove lid, & vadas are swelled up well with pores on it. Apply oil on each vada & flip them over to roast it's other side. Then flip them over and let them cook on other side too. Till you see both the sides slightly browned.
Now medu vada is ready to serve. Serve hot with rassam, sambhar Or chutney.