Preheat the oven to 400 degrees Fahrenheit.
Wash your potatoes and add to a baking sheet. Poke a few holes in them with a fork. Bake for about 45-60 minutes or until the potatoes are easily pierced with a fork.
Remove from the oven and let cool until easy to handle.
Peel the skins off the potatoes and either pass through a potato ricer, mash really well with a potato masher, or use an immersion blender to puree the potatoes. All methods work, you just want to make sure there are no large potato chunks regardless of what you do. Add to a generously floured surface.
In a small dish, combine the flour, potato starch and salt.
Make a well in the middle and add in the egg in the center. Whisk the egg and then add the butter and incorporate all together until the butter has melted.
Add the flour mixture and use your hands or a bench scraper to fold all the ingredients together.
Form the dough into a ball. It should not be sticky, if it is, add more flour until it holds together without stickiness but does not seem dry. Since gnocchi gets boiled, you want it to be able to retain its shape and not get mushy.
Cut the dough into about 4-6 pieces. Take each piece and roll into a long rope, about 1 inch thick.
Cut the rope into bite sized pieces, about 1 inch in length. You can leave the gnocchi as is, or use a fork to roll it along the edge to create fork impressions.
Bring a pot of salted water to boil. Once boiling, add in the gnocchi, cooking in batches so you don't overcrowd the pot. Let boil for just about 2 minutes. It is done when the gnocchi floats to the top.
Drain and repeat with any remaining gnocchi. Serve with your favorite sauce and enjoy. I love my homemade pesto or pomodoro sauce.