Steam broccoli until very tender, about 8–10 minutes for fresh or 5–6 minutes for frozen, then drain well.
Add broccoli, butter, parmesan, and lemon zest to a food processor and blend until smooth.
Add warm water one tablespoon at a time until a soft, creamy consistency is reached. Taste and add salt only if needed, then spoon into a bowl.
Taste and add salt only if needed, then spoon into a bowl. Top with tender broccoli florets and a light sprinkle of parmesan if desired, and serve warm.
Notes
Drain broccoli thoroughly to avoid watery puree.Blend longer than expected for the smoothest texture.Add lemon zest gradually so it stays bright but not sharp.