Step #2 In a large heavy skillet or saucepan, melt the butter over med-heat/flame.
Step #3 Add the onion, jalapenos, coriander & cumin, stirring, & cook, garlic, for about 1 min.
Step #4 With a whisk, stir in the the flour & cook for about 1 min, stirring constantly & vigorously.
Step #5 Add the milk & continue to whisk until the mixture comes to a simmer, then stir every once in awhile until the sauce is thickened, 3 to 4 mins.
Step #6 Remove from the heat.
Step #7 Stir in the salsa & salt & set aside.
Step #8 Meanwile, bring a large pot of water to a boil & cook the shell pasta according to the package directions until done.
Step #9 Drain well.
Step #10 In a very large bowl, mix together the pasta & sauce, then fold in the Jack & Cheddar cheeses until well mixd.
Step #11 Place the mixture in a lightly buttered 9 by 13 inch baking pan.
Step #12 In a small bowl, mix together the crushed chips & Parmesan, then sprinkle evenly over the top of the mac & cheese.
Step #13 Bake in the oven for 20 to 30 mins, the sides are slightly bubbling, or until the pasta is heated through, & the top is golden brown.
Step #14 I like to use pickled, jarred jalapenos because of their consistent heat.
Step #15 You can certainly use fresh or canned, but be sure to take a little taste & adjust the amount to your heat preference.