Yes, PORTERHOUSE is a Scrabble word!

Letter values in Scrabble US: P 3, O 1, R 1, T 1, E 1, R 1, H 4, O 1, U 1, S 1, E 1.

Is it a valid word?

PORTERHOUSE is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

large steak from the thick end of the short loin containing a T-shaped bone and large piece of tenderloin

Also: porterhouse steak.