I took this (we had leftovers so I froze) out of the freezer last night. What's the best way to re-heat/serve?

I have not made this particular gnocchi recipe, but I am assuming that you have frozen them uncooked? If so, just add them to the boiling water frozen. Don't defrost them or they will all congeal together -- I have unfortunately learned not to defrost frozen gnochhi from experience! They shouldn't take too much longer to cook then fresh gnocchi. After the gnocchi have cooked (they will rise to the top of the boiling water), then you can sauce and serve them. What a great thing to have in your freezer. Enjoy!