Bring a large pot of water to a boil. Peel and cook potatoes until until soft, 20-30 minutes. Drain and set aside.
While potatoes cook, melt 1 tablespoon butter in a large skillet. Add sliced mushrooms and saute until mushrooms release their liquid and begin to brown.
Add garlic and cook until fragrant. Stir in chopped parsley and red pepper flakes if using them. Remove from heat and set aside. Allow mixture to cool while you prepare the potato dough.
Place cooked potatoes in a large mixing bowl. Add eggs, grated parmesan cheese, flour, salt and pepper. Mix until well combined and you have a smooth dough.
Knead dough and keep adding a little flour at a time until you have a dough that isn't too sticky and is easy to roll out and work with.
Flour work surface and use a rolling pin to roll out potato dough to about ¼ inch thickness.
Use a cookie cutter to cut out an even number of 3 inch circles.
Place a couple tablespoons mushroom/garlic/parsley mixture in the center of a potato circle, and add a tablespoon of shredded provalone cheese.
Top with another potato dough circle. Carefully pinching edges together with your fingers to seal in mushroom/cheese mixture.
Heat another tablespoon of butter in a skillet and fry on each side until golden brown.
Serve immediately topped with a dollop of sour cream and a sprinkle of chives if desired.