Bring a large saucepan of water to a boil, and add about a teaspoon of salt. Prepare a large bowl filled about halfway full with ice water to keep beside the stove. Add 1 pound fresh baby spinach to the boiling water, and cook until just wilted and bright green, about 1-2 minutes. Immediately transfer the spinach to the ice bath to stop the cooking. Note that I like to do this in 3 batches to ensure that the spinach blanches evenly and none becomes overcooked. Transfer the spinach to a colander to drain and discard the water.
Transfer the blanched spinach to your blender. Add the chopped tomato, 1 1.5 inch piece ginger, and 4 of the garlic cloves. Turn the blender on high, and blend until smooth, pausing to scrape down the sides of the blender as needed. Set aside.
You can either cook the palak paneer in the same saucepan you used to blanch the spinach, or you can use a skillet or saute pan. Heat the pan over medium heat, and add 1 1/2 tablespoons canola oil. Add the chopped onions and 1 teaspoon kosher salt and cook until the onions are soft and translucent.
Add the remaining 2 cloves of minced garlic, 1 teaspoon garam masala, 1/4 teaspoon turmeric powder, and 1/8 teaspoon cayenne pepper (if using). Cook until fragrant, about 1 minute. Add 1/2 cup of water, then pour in the spinach mixture from the blender. Bring to a boil, then reduce to a simmer (medium-low heat) and continue to cook, stirring often until slightly thickened and reduced. Stir in 3 Tablespoons heavy cream and paneer and cook until heated through, about 2 minutes. Serve with basmati rice, naan bread, or parathi.
Notes
Instead of using fresh spinach, you can use frozen spinach (chopped or whole). Try to aim to use close to 1lb, but if you happen to have a 10oz package on hand (they're often sold in 10oz "bricks"), just use that instead and cut the rest of the ingredients in half. Or make the recipe as-is with two 10oz bricks.To use the frozen spinach, skip the blanching in step 1. Simply thaw the spinach on a plate (in the fridge overnight or in the microwave), and add it straight to the blender. Follow the rest of the recipe as written.