How to counter bitterness in dal recipe I just made the recipe below for slow cooker dal and there is quite a bitter flavor. I'm wondering:
- what ingredient would cause this bitterness and why?
- is there something I can add to counter the bitterness?

2 teaspoons whole cumin seeds
2 teaspoons whole mustard seeds
1 teaspoon whole fennel seeds
2 cups split red lentils, rinsed
5 cups water
1 (15-ounce) can diced tomatoes
1 medium onion, diced
1-inch piece fresh ginger, peeled and finely grated
1 tablespoon ground turmeric
1 bay leaf
1 teaspoon kosher salt
1/4 teaspoon freshly ground black pepper
Fresh cilantro leaves, for serving (optional)
Jasmine rice, for serving


Add the cumin, mustard, and fennel seeds to a small sauté pan, and place on the stove over low heat. Toast the seeds, using a wooden spoon to stir frequently, until fragrant, 3 to 4 minutes.

Add the toasted spices, lentils, water, tomatoes, onion, ginger, turmeric, salt, and pepper in the bowl of a 6-quart slow cooker. Stir together. Cover the slow cooker with the lid, then set to low and cook for 4 to 6 hours, or high and cook for 2 to 3 hours, until most of the liquid has been absorbed and the lentils are soft. Stir before serving.
In dal recipes I have made, the lentils and tempering are cooked separately, then combined later.  They generally begin by toasting spices (careful, mustard pops, but that is what you want), then caramelizing thinly sliced onion in the spices.  This brings out the sweetness of the onion, which can offset the bitterness of some of the spices.  Once the lentils are cooked, the tempering (onion and spices) is added and the seasoning is adjusted.