Step 1

Pour 1 cup of the flour onto a work surface. Add cold mashed potatoes, and create a well in center of potatoes. Crack egg into the well, and whisk lightly with a fork. Sprinkle with 1/4 teaspoon of the salt. Use hands to combine ingredients and create a dough. Add remaining flour, as needed, to keep dough from sticking. Do not over work the dough.

Step 2

Divide dough into 4 to 6 portions, and roll each portion into 3/4-inch wide “logs”. Using a knife or bench scraper, cut each rope into 1/2 to 3/4-inch pieces.

Step 3

Flour the back side of a fork. Working with 1 piece at a time, roll gnocchi down back side of fork to create small ridges. Repeat with remaining gnocchi, and chill 10 minutes.

Step 4

While gnocchi chills, bring a pot of salted water to a boil. Cook gnocchi in batches in boiling water until all pieces are floating, about 4 minutes. Use a slotted spoon to transfer gnocchi to a plate in a single layer.

Step 5

Melt butter in a large non-stick skillet over medium-high. Add boiled gnocchi to hot skillet; cook, stirring occasionally, until lightly toasted and golden, 2 to 3 minutes. Sprinkle with Parmesan, pepper, and remaining salt.