On a quest to make real Mexican salsa

I love hot salsa, not the chunky mild stuff, but the kind that is dark red and smooth and spicy. I've only gotten the good stuff out of big jugs at taco stands or served with chips in hole-in-the-wall Mexican restaurants.*

My new mission is to learn to make this simple, proletarian (read: no mangos) kind of salsa for myself. Sadly, I can't figure it out just by taste. I do know it's not just chopped-up tomatoes, jalapenos, onions, cilantro, and lemon juice -- those are the ingredients in your standard Internet recipes for salsa, but you will just end up with pico de gallo.

A Google search in Spanish (after looking up the word for recipe, receta), has led me to a recipe that looks pretty promising. My Spanish is not good, but I can tell that this recipe involves vinegar and cooking the salsa.

The recipe is pasted below, in case some kind person would like to translate it for me. Otherwise, my next post will be my attempt at a translation, with a dictionary's help, and maybe a report on my attempt to make this salsa.

Ingredientes:

2 cebollas picadas.
3 pepinillos en vinagre.
50 gr. de mantequilla.
4 cucharadas de vinagre.
4 cucharadas de vino blanco.
6 cucharadas de salsa de tomate.
1 cayena picada.
Perejil.
Sal.

Preparación:

Poner la cebolla picada en un cazo junto con el vinagre y el vino blanco.
Cocer a fuego lento hasta que se consuma el líquido a la mitad.
Añadir los pepinillos picados, la salsa de tomate, la cayena y la sal. Dejar
cocer 10 minutos más.
Agregar el perejil y la mantequilla, remover.
Sirve para acompañar carnes asadas o a la brasa.

Link to the recipe

* The Chinese equivalent of is that homemade, oily chili brew in the tabletop condiment jar of your local Chinese eatery.