Begin by peeling and chopping the Russet or Yukon Gold potatoes into even chunks. Place them in a large pot filled with salted water and bring to a boil. Cook for 15-20 minutes, or until the potatoes are fork-tender. Drain the potatoes well and return them to the pot to let any excess moisture evaporate.

While the potatoes are boiling, preheat your oven to 425°F (220°C). Line a baking sheet with parchment paper.

In a small saucepan or microwave, melt half of the unsalted butter and gently warm the heavy cream until it’s hot but not boiling. Set aside.

Drain the cooked potatoes again and return them to the pot. Using a potato masher, mash the potatoes until completely smooth. Stir in the warmed butter, cream, grated Parmesan, salt, and black pepper, mixing until well combined. Fold in the egg yolks.

Transfer the velvety potato mixture into a piping bag fitted with a star tip. Pipe generous mounds onto the prepared baking sheet.

Brush the tops of each piped mound with the remaining melted butter. Place the baking sheet in the preheated oven and bake for 15-20 minutes, or until golden and crispy outside.

Remove from the oven and let cool slightly. Sprinkle with freshly chopped chives or parsley and sea salt.