1 cup lentils or split peas
1 cup vegetables (your choice, eg. potatoes, carrots...), chopped
3 cups water
2 Tbsp. butter
1/2 tsp. mustard seeds
1 onion, finely chopped
2 cloves garlic, finely chopped
1/2 tsp. turmeric
1/4 tsp. cayenne pepper or chili powder
1 tsp. garam masala
1 tsp. salt
1 tomato, chopped
1 Tbsp. fresh cilantro or coriander, finely chopped (optional)

Bring water to a boil.  Add lentils and vegetables.  Simmer, covered, until lentils are very soft, stirring occasionally, adding water as necessary.

Heat butter in a small pan and fry mustard seeds until start to pop and crackle.  Add onion and garlic.  Saute for a few minutes, then add spices, salt and tomatoes and cook til soft, about 5 minutes.

Stir into lentil soup and simmer 5 more minutes.  Garnish with cilantro before serving.