Into a large pot pour about 4 quarts of heavily salted water, cover and set over high heat.
Measure the milk in a glass measuring cup and warm for a minute in a microwave on high (or warm in a small saucepan).
In a medium-size saucepan, melt the butter over medium heat, then stir in the flour and whisk until the mixture turns deep gold, about 2 minutes.
Add the warmed milk all at once and continue to whisk constantly until the mixture thickens and comes to a full boil, 4 to 5 minutes. (Whisk diligently and there will be no lumps.) Stir in the salsa, remove from the heat, then add the cheese and stir until it melts. Taste and season with salt.
When the water comes to a boil, add the dried pasta. Stir well so no pieces stick together and boil until the pasta is al dente, 8 to 10 minutes. Drain thoroughly and return to the pot.
Stir in the cheese sauce, then spoon into a serving dish. Sprinkle with the cilantro and you're ready.