Bring a large pot of salted water to a boil and cook the pasta according to package directions until al dente; drain well in a colander without rinsing.
While the pasta cooks, melt the butter in a saucepan over medium heat and let it foam; skim off the foam with a spoon as needed.
Continue cooking the butter, swirling the pan occasionally, until the milk solids turn golden brown and give off a nutty aroma; remove from heat immediately to prevent burning.
Place the hot drained pasta in a large mixing bowl, pour the browned butter over it, then add the grated mizithra and Romano cheeses.
Toss everything together until the pasta is thoroughly coated and the cheeses begin to melt into the butter; adjust seasoning if desired.
Transfer to plates, sprinkle with the minced parsley, and serve immediately.
Notes
If butter is taking too long to brown: increase heat slightly.
If butter browns too quickly: remove from heat immediately.
If butter burns: start over because burned butter cannot be saved.
Signs of properly browned butter: golden brown color and nutty aroma with brown bits at the bottom.
Can’t find Mizithra? Use Parmesan cheese instead.
For a sharper flavor: increase the ratio of Romano.