Boil pasta shells in salted water until slightly firm, according to package directions.
In another saucepan, combine the milk, Parmesan, cheddar, and butternut squash over medium heat until melted and combined. Turn off the heat. Add salt, mustard, pepper, Worcestershire sauce, and chili powder or Tabasco.
Drain the pasta but don’t rinse it. Add it to the cheese sauce and toss to coat the pasta.