Step 1

In a large pot over medium, melt the butter. Add the cumin seeds and cook, stirring, until fragrant, about 30 seconds. Add the onion, ginger, cilantro stems and ½ teaspoon salt; cook, stirring occasionally, until the onion is soft and starting to brown, 13 to 15 minutes.

Step 2

Add the potatoes, turmeric, ½ teaspoon each salt and pepper, and 3 cups water. Bring to a simmer over medium-high, scraping up any browned bits. Reduce to medium and cook, uncovered and stirring occasionally, until the potatoes are tender, 15 to 20 minutes. Add the spinach and cook, stirring occasionally, until heated through, 1 to 2 minutes.

Step 3

Off heat, stir in the cilantro leaves, then taste and season with salt and pepper.