1) Mix together mashed potatoes and yolk with a fork until it’s well combined.
2) Add in flour and mix well until the flour is incorporated. You should be left with a fairly dry dough. It shouldn’t be sticky at all. If it is, add more flour a few tablespoons at a time.
3) Turn dough out onto a lightly floured surface and cut it into 4 even pieces.
4) Working with one piece at a time, roll the dough out into a long strand about 1/2 inch wide in diameter. Try to get it as even as possible, but it’s okay if it’s not perfect.
5) Use a dough scraper to chop the strand of dough into 1 inch dumplings.
6) Once your dumplings are chopped, use the back of a fork to gently press into the gnocchi and make some grooves.
7) Once all the gnocchi are made, cook them in simmering salted water. They are done when they float, about 3-4 minutes.
8) For butter sauce, melt butter in a large skillet. Once melted, add cook water, herbs, and spices, and stir well. Toss drained gnocchi with the sauce and serve immediately!