The polenta that I get is quick-cooking (not instant) and cooks in 5 minutes, after starting to boil. You may have to adjust the time of the dish according to the type of polenta you have.
You can substitute oregano or rosemary for the sage if you prefer.
If you don’t have whole sage leaves, use 1 tbs crumbled.
Keywords: polenta gratin, butternut squash, squash gratin