Peel, chop, and place your Russet or Yukon gold potatoes in a large pot. Cover with cold salted water and bring to a boil over high heat. Reduce to medium and simmer for 15-20 minutes, or until fork-tender. Drain well.

Preheat your oven to 425°F (220°C). Line a baking sheet with parchment paper.

In a small saucepan, melt 2 tablespoons of unsalted butter. Warm 1/4 cup of heavy cream in the microwave for about 30 seconds without boiling.

Return the drained potatoes to the pot and mash them until smooth. Stir in melted butter, warmed cream, Parmesan cheese, salt, and black pepper. Mix in egg yolks until fully combined.

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

Brush the tops of the piped mounds with remaining melted butter. Bake for 15-20 minutes, or until golden brown and crispy.

Remove from the oven and serve immediately, garnished with fresh chives or parsley and sprinkle with sea salt.