Pat the tofu dry and break into large chunks while you place the chunks into a high speed blender or smoothie maker.
8 ounces firm tofu
Add the lime juice, jalapeno, cilantro, water, salt, and pepper.
3 Tablespoons fresh lime juice, ½ medium jalapeno, 1 cup fresh cilantro, leaves and stems, ⅓ cup water, ¼ teaspoon salt, ¼ teaspoon pepper
Blend until fully pureed.
Taste and season to your liking with more salt and pepper, depending on what you're serving it with.
Notes
I recommend using a high speed blender or smoothie maker over a food processor. A food processor will work if that's all you have, but the texture won't be as smooth.
To make the sauce mild, remove the seeds from the jalapeno or omit it completely.
To make the sauce spicier, swap the jalapeno for a serrano or habanero pepper.
If you'd rather not use tofu, go ahead and use sour cream, but don't add the water.
You will need to adjust the salt and pepper level to taste at the end depending on the dish you will serve the sauce with.
Add a small garlic clove to the sauce before pureeing if desired.
For a stronger lime flavor, add a teaspoon of lime zest to the sauce before pureeing.