1 teaspoon (3g) Diamond Crystal kosher salt; if using table salt, use half as much by volume or same weight
2 tablespoons (30ml) heavy cream
Combine spinach with 1/2 cup (120ml) water in a 3-quart saucier and place over high heat. Bring water to a boil, cover, reduce heat to medium-low, and cook until spinach is completely wilted, about 5 minutes. Transfer contents of pan to countertop blender and blend on high speed until completely smooth, about 1 minute. Set purée aside.
Wipe out saucier with clean kitchen towel or paper towel. Add 2 tablespoons of oil to the saucier and place over medium-high heat until shimmering. Add half of the paneer pieces and cook, flipping once, until golden, about 2 minutes. Transfer paneer to plate and repeat with remaining paneer pieces. Add remaining tablespoon of oil to pan along with cumin and mustard seeds and cook until seed begin to pop, about 30 seconds. Add garlic, stir, and cook until aromatic and pieces start to take on some color, about 30 seconds.
Pour spinach purée into saucier, season with salt and chilli powder, and stir to combine. Add cooked paneer and cream, stir, and serve immediately.