Wash the spinach thoroughly under running water to remove any dirt or grit. Trim off any thick stems if desired.
Bring 4 cups of water to a rolling boil in a large pot.
Add the spinach and cook for 1–2 minutes, just until the leaves are wilted and bright green.
Using a slotted spoon or tongs, immediately transfer the spinach to a bowl filled with ice water.
Let it sit for 2–3 minutes. This stops the cooking process and helps preserve the vibrant green color.
Drain the spinach and gently squeeze out excess water.
Transfer it to a blender or food processor. Blend until smooth, adding 2–4 tablespoons of water as needed to help it blend.
For an extra silky puree, blend for an additional 30–60 seconds.
Use immediately in your favorite recipes, or store for later.