Peel potatoes and cut into fourths. Put in a large pot and cover potatoes with cold water and add the salt.
Bring to a rolling boil and let gently boil for about 20 minutes or until potatoes are fork-tender.
Drain potatoes in a colander.
Add the butter to the pot and let melt while the potatoes drain. Add the potatoes back to the pot and add the half and half. Mix with the hand mixer until creamy and smooth, add the egg yolks, a handful of chives, and salt and pepper to the mixture. Stir well with a wooden spoon.
Using the star tip, fill the piping bag with the potato mixture and form tennis ball mounds on a baking sheet topped with parchment paper.
Bake the potatoes in the oven at 450° for about 20 minutes.
Notes
I made the potatoes ahead of time, covered them with press and seal, and stored them in the refrigerator until I was ready to bake them.