Rinse the yellow split peas until the water runs clear. This keeps the dal smooth and avoids grainy surprises.
In a pot, melt the butter or heat your fat of choice. Add the onion and cook until translucent and slightly golden, 4–5 minutes.
Add garlic and ginger; sauté for another minute until fragrant. Your kitchen should smell like a spice market now.
Stir in cumin seeds (or ground cumin), turmeric, coriander, and chili powder. Toast briefly to wake up the spices—about 30 seconds.
Add the chopped tomato and cook until it softens and blends in. It’s okay if it looks a little saucy—dal loves that.
Pour in the rinsed peas and water or stock. Bring to a gentle boil, then reduce heat and simmer uncovered for 25–30 minutes, stirring occasionally, until the peas break down and the dal becomes thick and creamy.
Season with salt. If you like a brighter pop, finish with a squeeze of lemon or lime and a handful of chopped cilantro.