Heat oil or butter in a small pan. Add the chopped onions. Saute till light brown.
Then add the remaining ½ tablespoon of the chopped ginger and garlic, along with the chopped chilies. Stir and mix well.
Saute till the onion becomes golden.
Add the tomatoes and saute till the oil starts to leave the sides of the mixture.
Pour this mixture along with the oil in a the cooked lentils.
Stir and add salt as required. Simmer for 4 to 5 minutes or more till the dal thickens.
While simmering if the dal amritsari looks more thick, then you can stir in some water and continue to simmer.
Once done, then garnished with 6 to 7 whole or chopped mint leaves.
Top the dal with some butter. Serve dal amritsari garnished with mint leaves and topped with some butter.