Sweet Potato Gnocchi

Ingredients:
1-1/2 lbs Sweet Potatoes
1/2 lb Yukon Gold Potatoes (or any other white potato)
1 cup of Parmiggiano
1-1/2 to 2 cups of All Purpose Flour
2 Egg Yolks
Salt, to taste

Sauce:
1/2 cup of Unsalted Butter
10 leaves or so of Fresh Sage
Freshly Grated Parmiggiano to taste
Black Pepper to taste