From diesel
Found it!
Medardo's green stuff:
1/2 lb jalapeños (about 6-8)
1/4 of a large yellow onion
2 cloves garlic
1/2 cup corn oil
1 tsp course salt
Simmer whole jalapeños and onion in water until tender but not mushy, then drain and remove stems.
Blend jalapeños, onion, raw garlic and oil until smooth, then blend in salt to taste.
The oil holds in air bubbles, which gives it the consistency, but it also means it goes bad relatively quickly. I usually keep it in the fridge and toss it after 4 or 5 days because the quality goes downhill.