Buttermilk is lightly spiced with fenugreek, cumin, asafoetida and mustard seeds. It's excellent served as an accompaniment with curried lentils/daal.
If you do not like the taste of fenugreek seeds, you can use fenugreek powder instead. Roast the fenugreek seeds and use 1/2 teaspoon of the powder.
Can be found in Indian/South Asian stores. If unavailable, substitute in dried curry leaves.