> 2 lbs russet or Idaho potatoes, peeled and cut into 1/2-inch chunks
> 4 tbsp unsalted butter, melted and cooled
> 1/4 cup light sour cream
> 1/3 cup finely grated Parmesan
> 2 large egg yolks
In a large pot, combine the potatoes and enough cold water to cover by 2 inches. Season generously with salt. Partially cover and heat to a boil on high. Reduce heat to simmer. Simmer 10 min., until tender.
Meanwhile, preheat oven to 400°F. Line 2 baking sheets with parchment. Fit a jumbo star tip into a piping bag.
In a medium bowl, whisk together the butter, sour cream, Parmesan, and yolks until well combined. Drain the potatoes well and return to pot. Mash until smooth. Season with salt to taste.
To pot, gently stir in butter mixture. Season generously with pepper. Transfer potato mixture to piping bag and pipe into rosettes onto prepared baking sheets. Bake 25–30 min., until golden brown. Serve warm.
To make ahead, pipe rosettes and then freeze. Bake in 375°F oven for 35–45 min., until hot in centers.