Place jalapenos, garlic, and onion in a pot. Cover with water. Bring to a boil, then reduce to a gentle simmer. Cook 10–12 minutes until jalapenos turn dull green and slightly soft. This tames raw harshness but keeps heat.

Turn off heat. Use a slotted spoon or tongs to lift jalapenos, garlic, and onion from hot water. Let them cool 5 minutes on a plate. This short cooling time helps blend safely and keeps flavors bright.

For milder salsa, slice jalapenos lengthwise and remove some seeds and membranes. For true taqueria fire, leave seeds in. I usually keep half the seeds. That gives bold heat without burning your lips off.

Place cooked jalapenos, garlic, and onion into blender. Add lime juice, 1/4 cup water, salt, and cumin if using. If you like cilantro flavor, add a small handful now. Keep a little space at top of blender.

Start blending on low, then increase to high. While blender runs, slowly pour in the neutral oil in a thin stream. The oil emulsifies with jalapeno mixture and turns it creamy. Blend 1–2 minutes until silky and thick.

Stop blender. Taste a small spoonful. Add more salt if it tastes flat. Add extra lime juice if you want more brightness. If salsa is too thick, blend in a tablespoon of water at a time until it pours easily but still coats a chip.

Pour salsa into a glass jar or squeeze bottle. Refrigerate at least 1 hour before serving. This rest time lets flavors marry and sauce thicken slightly. Serve cold or cool with hot tacos, chips or grilled meats.