Peel and dice the potatoes into roughly 1-inch chunks, then rinse and set aside. Finely chop the onion and measure out your spices and tomatoes.
Heat the oil in a large heavy-bottomed pan over medium heat until shimmering. Add the cumin seeds and cook until they crackle and turn golden, filling the kitchen with a warm, toasted aroma.
Add the chopped onion to the pan and sauté, stirring occasionally, until it softens and turns a light golden color, about 5-7 minutes. The onion should smell sweet and fragrant as it cooks.
Stir in the diced potatoes, coating them with the spiced oil and onion mixture. Cook for about 3-4 minutes, allowing the potatoes to start developing a slight color.
Pour in the canned diced tomatoes along with their juice, stirring to combine everything evenly. Increase the heat slightly and let the mixture simmer uncovered for about 10 minutes, until the potatoes are tender and the sauce thickens a little.
Sprinkle in the garam masala, turmeric, and a pinch of salt. Stir well and cook for another 2 minutes to allow the spices to bloom and deepen their aroma.
Stir in the frozen peas, mixing thoroughly. Cook for 3-4 more minutes until the peas are bright green and heated through. If the curry seems too thick, add a splash of water and simmer briefly to loosen it.
Taste and adjust the seasoning with additional salt if needed. Remove from heat and let the curry rest for a couple of minutes to allow flavors to meld.
Serve the pea and potato curry hot, garnished with fresh herbs if desired, alongside rice or flatbread for a comforting meal.
