Dal is typically made from split lentils or split peas, although other recipes use split chickpeas (chana dal) or kidney beans (rajma dal). For this recipe, I recommend sticking with red split lentils (masoor dal), yellow split lentils (moong dal), or even yellow split pigeon peas (toor dal) if you have them on hand (affiliate links). The cook time will vary slightly depending on which one you choose.  And of course, you can always use regular red lentils, sold at most grocery stores (they take just a bit longer to cook and soften).