Heat oil in a pan and add cumin seeds. When it sizzles, add onion and fry till soft. Add green chillies, salt and fry for a minute. Remove from heat and add coriander leaves. Allow to cool.
In a large bowl mix 1 cup flour, instant dried yeast and sugar. Microwave milk and water for 30 seconds or until its lukewarm and add to flour. Mix with a spatula.
Then add the melted butter, salt and mix with a spatula. Add remaining flour little by little and mix with a spatula to form a sticky dough.
Transfer the dough to a generously floured surface and knead the dough for 8-10 minutes or until the dough is non-sticky and smooth.
Now flatten the dough with your hands to form a rectangle. Put the onion mixture, fold from all sides and seal well.
Knead for another 12-15 minutes or till the onion mixture is well incorporated in the dough, adding more flour if required.
Grease a large bowl with oil and place the dough in it. Cover and keep in a warm place for 1 - 1 ½ hours or until the dough doubles in size.
Once the dough has risen, knead for another 8-10 minutes, to remove any air bubbles. Divide into 8 equal portions and shape them into buns.
Place them on a baking tray lined with parchment paper. Cover and keep in a warm place for 45 minutes - 1 hour.
Preheat the oven to 200 C | 400 F for 10 minutes. Brush the tops of buns gently with milk.
Bake them at 180 C | 350 F for 15-18 minutes or until the buns turn golden. After removing from oven, brush them with melted butter.