Cook pasta in a large pot of salted boiling water until al dente. (about 1-2 minuites less than package instructions because it will continue to cook in the oven.) Drain and set aside.
2.Meanwhile, melt butter in a medium pot over medium heat. (The pot should be large enough to hold all the pasta and cheese sauce when cooked.)
Whisk in flour and cook, whisking constantly, until little bubbles start forming and the flour begins to turn golden, about 4 minutes. Slowly whisk in milk to avoid clumping. Add onion powder, salt and mustard powder. Bring to a simmer, whisking constantly and being sure to get around the edges of the pot to avoid burning.
Add grated cheeses and cream cheese and whisk to blend until the cheese is completely melted.
Heat oven to 400 degrees. Line a rimmed baking sheet with aluminum foil (to catch any dripping cheese.
Put the cooked and drained macaroni in the pot with the cheese sauce and mix to combing. Transfer to a baking dish (about 9x13)
Place on prepared baking sheet and bake until macaroni and cheese is bubbling, about 15 to 20 minutes. Optional: sprinkle with some extra cheese and broil for the last 3-4 minutes.
Let cool slightly before serving.