Peel and chop potatoes into chunks, boil in salted water for 15-20 minutes until fork-tender, then drain.

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

Melt 2 tablespoons of unsalted butter and warm heavy cream in a small saucepan over low heat.

Mash drained potatoes until smooth, then mix in melted butter, warm cream, Parmesan, salt, and black pepper, followed by egg yolks.

Transfer mixture to a piping bag and pipe rosettes onto the baking sheet.

Brush piped potatoes with melted butter and bake for 15-20 minutes until golden brown.

Garnish with sea salt and chives or parsley before serving.