Bring a pot of water to boil for the potatoes. Saute the onion in a small pan in 2 tablespoons of butter until translucent and set aside. Boil the potatoes until tender.
While the potatoes are boiling, begin the dough. Whisk together the eggs, 1/4 cup water and sour cream and pour into a small pitcher (or you can actually whisk them right in a container such as a 2-cup glass measuring vessel). Mound the flour in the center of a clean room-temperature work surface like a large wooden cutting board. Create a crater in the center of the mound. Pour enough of the egg mixture into the center to fill the crater. With a fork, gently begin to scramble the mixture within the confines of the crater, whilst integrating the flour from the sides of the crater as you carefully beat the egg mixture.
Once this first amount of the egg mixture is mostly mixed in, shore up the sides of the mound again with flour, maintaining the crater shape. Repeat the process with a second pour of egg mixture into the crater, and again until you have combined all the egg mixture. (Remember that making pasta is not an exact science. Depending on the flour, you may need more moisture to make the dough come together, in which case use a little extra milk or water. Conversely, if the dough is too wet, add a little more flour - but just enough to make it the right consistency. This is an acquired skill so be patient with yourself.) Start kneading the dough with your palms, allowing the warmth of your hands to impart elasticity to the dough. Knead for a count of about 400 strokes or until you feel you have created a cohesive mass. Wrap the dough in plastic wrap and allow it to rest for about 30 minutes.
Return to the potatoes, drain, and mash them with the sauteed onion, chives, butter, milk, and salt and pepper, to taste. Set aside.
Work with 1/3 of the pasta dough at a time - keeping the balance wrapped in plastic wrap to prevent it from drying out. Use a pasta machine to gradually roll each section of the pasta down, successively reducing the setting on the machine until it is at a thickness of 1/16th of an inch.
Cut 3-inch circles of pasta, spoon some of the mashed potatoes into the center and fold the filled circles into half moons, sealing the edges with egg wash and pressing shut with your fingers or carefully with the times of a fork.
Bring a large shallow saute pan of water to a boil, and gently boil the pierogi in batches for 2 or 3 minutes, removing carefully to a utility platter with a wooden spoon.
The final step is to melt the butter in a large fry pan and saute the garlic for a few minutes until it is tender and imparts its flavor to the butter in the pan. Be careful not to burn either the butter or the garlic. Saute the pierogi in this garlic butter and serve.
Recipe courtesy of Robert Irvine with Brian O'Reilly. Harper Collins Publishers, copyright 2007