Place lentils in a small-medium bowl and fill with water. Use your hand to swirl the dal around until the water becomes murky. Tip the bowl to take out the excess water and repeat until the water runs clear. Remove any debris and strain the excess water.
In a medium pot, add dal along with 3 ¼ cups (~769 ml) of water. Bring this to a boil over medium-high/high heat. Once it comes to a boil, reduce the heat to low-medium so that it simmers. Use a slotted spoon to remove any white scum that rises to the top of the pan. Cover with the lid ajar. Cook, stirring occasionally, for 30 minutes (See Note 1), until the dal has no bite to it and can easily be mashed. Top with ¼ cup water if you feel the dal is getting too thick. Turn off the heat.
INSTANT POT Add lentils along with 1 ½ cups (355 ml) of water. Select Pressure Cook - Low setting and set the timer to 7 minutes. Manually release the pressure.
In a separate large pan, heat oil over medium-high heat. Once hot, add the cumin seeds and sauté for about 15 seconds. Add the onions and sauté until slightly golden, about 7 minutes (See Note 2). Add the garlic and ginger and continue to sauté until the raw smell disappears (~30 seconds). Add the tomatoes, green chili pepper, and spice powders (cumin, coriander, red chili, turmeric) and salt. Cook until soft and you see the oil leaving the sides, about 3 minutes.
Stir the cooked dal into the tarka. Add 1 cup water (more or less), depending on how thick the dal got while cooking and how runny you like the consistency. Mix to combine.
Bring the dal to a simmer. Allow the dal to reduce and the flavors to meld for about 5 minutes, or until you achieve the desired consistency. Taste and adjust salt, if needed.
Add in the ghee or butter. If using fenugreek leaves, crush them between your hands and sprinkle into the dal. Turn off the heat. Add lemon juice, chopped cilantro, and garam masala, if using. Give it a stir.
Serve dal hot with rice, roti, naan or anything else your heart desires. I like to serve it with a mix of chopped onions, carrots, and cucumber on the side.