Place the cubed Yukon Gold potatoes into a large pot and cover them with cold water. Add a generous pinch of salt. Bring to a boil over medium-high heat and cook until the potatoes are fork-tender, about 15-20 minutes.
Drain the potatoes well in a colander, then return them to the pot. Heat them over low for about 2 minutes to steam off any excess moisture, which helps achieve a fluffy texture.
Using a potato ricer or masher, thoroughly mash the potatoes until smooth, ensuring there are no lumps.
Stir in the butter and mix until melted. Then, add the heavy cream, egg yolks, garlic powder, nutmeg, salt, and pepper. Mix until everything is well combined and creamy.
Preheat your oven to 400°F (200°C). Transfer the potato mixture into a pastry bag fitted with a large star tip. Pipe out small mounds onto a parchment-lined baking sheet, about 2 inches apart.
Bake in the preheated oven for 20-25 minutes, or until the tops are golden brown and crispy.
Once removed from the oven, garnish the Duchess Potatoes with finely chopped chives before serving warm.
Notes
For a richer flavor, consider adding cheese to the mixture.