Heat the oil in a medium-sized heavy pan over medium heat until shimmering. Add the cumin seeds and toast until they crackle and release a nutty aroma, about 30 seconds.
Add the chopped onion to the pan and cook, stirring frequently, until translucent and golden around the edges, about 5-7 minutes. You should hear a gentle sizzle and smell sweet caramelization.
Stir in the minced garlic and grated ginger, cooking for about 1 minute until fragrant and slightly softened. The mixture should smell warm and spicy.
Add the ground turmeric and coriander, stirring for 30 seconds to bloom the spices. Watch for a fragrant aroma and a slight darkening of the spices.
Stir in the diced potatoes, coating them well with the spice mixture. Cook for 5 minutes, stirring occasionally, until they begin to soften and turn slightly golden.
Pour in the chopped tomatoes and stir to combine. Cook, stirring frequently, until the mixture thickens and the oil starts to separate from the tomato-spice base, about 10 minutes. The sauce will look jammy and fragrant.
Stir in the green peas, then cover the pan and lower the heat. Let everything simmer gently for 10 minutes, until the potatoes are tender and the peas are heated through, with a vibrant green color.
Uncover and check the consistency. If the sauce is too thick, add a splash of water and stir; if too runny, simmer uncovered until it thickens slightly. Taste and add salt as needed.
Remove from heat and let sit for a few minutes to deepen the flavors. Garnish with chopped cilantro if desired.
Serve the warm pea and potato curry alongside rice or flatbread, enjoying the comforting aroma and vibrant flavors of this simple, soulful dish.
