Prepare the Lentils: Start by rinsing the red lentils and yellow split mung beans thoroughly under cold water until the water runs clear. This step is essential to remove any dust or impurities and to ensure a smooth texture for your soup. I soak mine overnight after washing.
Cook the Lentils: In a large pot, combine the rinsed lentils and mung beans with about 6 cups of water. Bring to a boil over medium-high heat, then reduce the heat to low and let it simmer. Skim off any foam that rises to the surface for a clear broth.
Add the Aromatics: While the lentils are simmering, heat the ghee in a small pan over medium heat. Add the grated ginger and turmeric roots, sautéing until fragrant. Next, toss in the chopped Thai chiles, fresh curry leaves, and crushed black cardamom pod. Sauté for a few minutes until the spices release their aromas.
Combine and Simmer: Once the aromatics are ready, add them to the pot of simmering lentils. Stir well to combine all the flavors. Continue to simmer the soup for another 20-30 minutes, or until the lentils and mung beans are tender and the flavors have melded together beautifully.
Final Touches: Taste the soup and adjust the seasoning with salt as needed. If you prefer a thinner consistency, you can add a bit more water or broth. Serve the soup hot, garnished with additional curry leaves or a drizzle of ghee for extra richness.