I made this tonight actually. Used Alton Brown’s recipe from his new Good Eats Reloaded show. No idea how true to form it was but it was great. 100 grams of pecorino to 50 grams of parmigiana. He makes a cheese paste in a bowl, then adds pasta water, then adds the pasta to it. No clumping or anything.
https://www.cookingchanneltv.com/recipes/alton-brown/cacio-e-pepe-5458695