Rinse the jalapenos and cilantro. Remove the stems from the jalapenos. For a milder sauce, slice the jalapenos in half and scrape out the seeds and white membranes with a spoon; for more heat, leave some seeds in. Roughly chop the jalapenos and cilantro so they blend more easily.
3-4 fresh jalapenos, 1/2 cup fresh cilantro leaves
In a blender or food processor, add the mayonnaise, sour cream, and buttermilk. If you prefer a thicker sauce, start with 1/4 cup buttermilk and add more later as needed.
1 cup mayonnaise, 1 cup sour cream, 1/2 cup buttermilk
Add the ranch dressing mix, garlic powder, onion powder, and a small pinch of salt. Pour in the lime juice and pickled jalapeno brine.
1 ounce ranch dressing mix, 2-3 tablespoons lime juice, 2 tablespoons pickled jalapeno brine, 1/4 teaspoon garlic powder, 1/4 teaspoon onion powder, salt
Add the chopped jalapenos and cilantro to the blender. If you are unsure about the heat level, start with 2–3 jalapenos and add more after tasting.
3-4 fresh jalapenos, 1/2 cup fresh cilantro leaves
Blend on medium-high speed until the mixture is smooth, creamy, and pale green, scraping down the sides as needed so no cilantro leaves remain unblended. If the sauce is too thick, blend in 1–2 tablespoons of milk or extra buttermilk. If using cotija or Parmesan, add it and blend briefly to incorporate.
1-2 tablespoons milk or extra buttermilk, 1-2 tablespoons grated cotija or Parmesan cheese
Taste the jalapeno ranch and adjust the seasoning: add more lime juice for brightness, a pinch more salt if it tastes flat, additional jalapeno or some seeds for more heat, or extra cilantro for a stronger herbal flavor.
3-4 fresh jalapenos, 1/2 cup fresh cilantro leaves, 2-3 tablespoons lime juice, salt
Transfer the sauce to a jar or airtight container. Cover and refrigerate for at least 1 hour, preferably 2–4 hours, to allow the flavors to meld and the ranch mix to fully hydrate.
Stir before serving. Use as a dip for tortilla chips and veggies, or drizzle over tacos, fajitas, burrito bowls, enchiladas, salads, burgers, or sandwiches.