Peel and chop the Russet or Yukon Gold potatoes into equal-sized chunks. Place them in a large pot, cover with salted water, and bring to a boil. Cook for 15-20 minutes, or until the potatoes are fork-tender. Drain thoroughly to eliminate excess moisture.

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

In a small saucepan, gently melt half of the unsalted butter over low heat. Add the heavy cream and warm it just until it's steaming but not boiling. Set the mixture aside.

Return the drained potatoes to the pot and begin mashing them until smooth and creamy. Stir in the warmed butter and cream mixture along with the grated Parmesan cheese, salt, black pepper, and egg yolks.

Transfer the creamy potato mixture into a piping bag fitted with a star tip. Pipe small mounds of the potato mixture onto the prepared baking sheet.

Brush the tops of the piped Duchess Potatoes with the remaining melted butter. Place the baking sheet in the preheated oven and bake for 15-20 minutes until golden brown and crispy on the edges.

Once baked, remove the Duchess Potatoes from the oven and let them cool slightly. Garnish with freshly chopped chives or parsley, and sprinkle a touch of sea salt on top. Serve immediately.