BRING A LARGE POT OF WATER TO A BOIL. SALT GENEROUSLY.
BOIL THE PASTA.
PICK THROUGH THE ARUGULA, REMOVING ANY LARGE, TOUGH STEMS. WASH AND DRY.
WHEN THE PASTA IS NEARLY DONE, SCOOP OUT A CUP OF THE PASTA WATER.
DRAIN THE PASTA. RETURN THE POT TO THE STOVE. LOWER THE HEAT TO MEDIUM.
MELT 2 TBPS OF BUTTER IN 2 TBSPS OF OLIVE OIL IN THE POT. GRIND IN A GENEROUS AMOUNT OF PEPPER. SALT JUDICIOUSLY.
STIR IN THE ARUGULA AND COOK FOR 30 SECONDS.
POUR IN 1/2 CUP OF PASTA WATER AND 1/2 CUP OF PARMESAN CHEESE. CONTINUE TO STIR VIGOROUSLY UNTIL YOU'VE ACHIEVED A CREAMY TEXTURE, ADDING MORE PASTA WATER IF IT GETS TOO THICK.
STIR IN THE RICOTTA UNTIL IT COATS THE PASTA.
SERVE IMMEDIATELY WITH THE REMAINDER OF PARMESAN ON THE SIDE.
SERVES 4