Put the milk in a medium pot over medium-high heat. While it’s heating, combine the lemon juice with ¼ cup plus 2 tablespoons warm water. When the milk comes to a boil, add the lemon juice mixture; the milk should immediately separate into curds and whey. Add a pinch of salt and cook, stirring, for 2 minutes. Line a strainer with a few layers of cheesecloth and put it in the sink; pour the milk mixture into the strainer to strain out the whey. Rinse the curds with cool water, then twist the edges of the cheesecloth around the cheese and squeeze out any remaining liquid. Transfer the cheese bundle to a plate lined with paper towels, weigh it down with a cast-iron skillet or another heavy object, and let rest for at least 3 hours.

Put 2 tablespoons of the ghee in a medium pot over medium heat. When it melts, add the cumin seeds and cook, shaking the pan occasionally, until fragrant, 1 to 2 minutes. Add the onion, garlic, and ginger and season with salt. Cook, stirring frequently, until the onions soften, 8 to 10 minutes. Add the jalapeños, coriander, paprika, and turmeric, and cook, stirring, until fragrant, about 1 minute. Add the tomatoes and cook, stirring occasionally, for 10 minutes. Add the spinach and continue to cook, stirring occasionally, until the spinach is tender, about another 10 minutes.

Meanwhile, heat the oven to 400°F. Unwrap the paneer and cut it into ¾-inch cubes. Melt the remaining 1 tablespoon ghee in an 8- or 9-inch square pan in the oven. Add the cubed paneer; toss gently to coat the paneer in the ghee and and season with salt. Roast, turning the cubes once or twice, until golden brown, about 15 minutes.

Stir the garam masala and cayenne pepper into the spinach mixture and cook for 2 minutes, then turn off the heat. Add the yogurt and cream to the spinach mixture and partially purée with an immersion blender. Stir in the roasted paneer. Taste and adjust the seasoning, then serve hot over basmati rice, if desired. (Store leftover palak paneer in an airtight container in the refrigerator for up to a week.)