It's best enjoyed right after cooking - storing and reheating gnocchi is tricky and changes the texture (they'll become a bit bloated as they continue to absorb the sauce) - but you can definitely refrigerate and reheat any leftovers. It will keep for 3 days in the fridge and is easy to reheat in the microwave or on the stovetop. Heat in 30-second intervals in the microwave, and reheat over medium heat for a few minutes in a pot on the stove. I like to add a little water when I'm reheating it, just to loosen the sauce up.