Fill a large pot with about 6 quarts water and place over high heat.
Warm the milk in a small saucepan over medium heat, or in a glass measuring cup in a microwave, for about 1 minute.
In a medium saucepan, melt the butter over medium heat, then stir in the flour—whisk until the mixture turns a deep golden, about 2 minutes.
Add in the warmed milk all at once and continue to whisk constantly until the mixture thickens and comes to a full boil, 4-5 minutes (whisk diligently and there will be no lumps).
Stir in the salsa, remove from heat, then stir in the cheese, stirring until cheese is melted.
Taste and season with salt.
When the water comes to a boil, add in pasta.
Stir so no pieces stick together; boil until pasta is al dente, about 8-10 minutes.
Drain pasta well and return to the pot.
Stir in the cheese sauce, then spoon mixture into a serving dish; sprinkle with cilantro.
*If you want a crusted macaroni and cheese—spoon mixture into a buttered baking dish; top with ½ cup bread crumbs mixed with 1 tablespoon melted butter and bake at 375° for 10-12 minutes, until richly browned and crisp.