In a large mixing bowl combine semolina, plain yogurt, and salt — add a small amount of water and stir into a thick batter.
Allow batter to rest for 15–20 minutes so semolina fully absorbs yogurt and water and swells to develop proper base texture — do not skip this rest.
While batter rests roughly chop approximately ¼ of a small red cabbage and blend with a small splash of water on high speed until completely smooth deep purple puree forms with no visible cabbage pieces.
Add ½ cup red cabbage puree to rested semolina batter and mix thoroughly until color is completely uniform and deep violet-purple throughout.
Heat 1 tablespoon coconut oil in a small pan over medium heat until shimmering.
Add dried red chilies and let sizzle for 15 seconds.
Add black mustard seeds and allow to fully splutter and pop completely before adding anything else — do not rush this step.
Add urad dal and chana dal and sauté stirring constantly for 30–45 seconds until light golden color develops.
Add fresh curry leaves — they will crackle and splutter dramatically in the hot oil which is correct.
Add grated ginger and chopped green chili and fry for another 30 seconds until fragrant.
Remove dried red chilies from tadka and discard or set aside.
Pour hot tadka directly into purple semolina batter and mix well until completely incorporated — batter should be fragrant deeply colored and well-seasoned.
Check batter consistency — should be thick but pourable similar to thick pancake batter — add small amount of water if needed.
Prepare idli cooker or steamer and grease molds generously with coconut oil or cooking spray.
Add one packet Eno fruit salt to batter along with a small splash of water and mix quickly and thoroughly — batter will immediately bubble and foam.
Pour batter into greased molds immediately while leavening reaction is still active — fill each mold approximately three-quarters full — do not wait after adding Eno.
Steam for 10–15 minutes until fully set firm to the touch and a toothpick inserted in center comes out clean.
Allow to cool in molds for 2–3 minutes then remove gently and serve warm with favorite chutney.