- 2 pounds Yukon gold potatoes
- 1 large leek (about 1 pound)
- 6 tablespoons butter, divided
- 1/4 cup white wine
- 1/2 cup heavy cream
- 1/2 cup whole milk
- 2 cups shredded cave-aged Gruyère cheese (about 1/2 pound)
- Salt and freshly ground black pepper
Place potatoes in a large pot and cover with water. Bring to a boil.
Reduce heat slightly and cook until tender, about 20 minutes.
Drain well, return to pot, and let steam for a few minutes.
While potatoes cook, slice leek in half lengthwise, then slice crosswise about 1/8-inch thick. Place in a large bowl of water and stir to loosen any trapped dirt. Lift leeks out of water.
Heat a large, high-sided sauté pan over medium-high heat. Melt 2 tablespoons butter, then add leeks. Season with salt and pepper. Stir occasionally for 7-10 minutes, or until leeks are tender and starting to brown. Add white wine, stirring to loosen any browned bits from bottom of pan. Add remaining butter, cream and milk and warm through. Remove from heat.
Mash potatoes to desired consistency. Add leek-cream mixture and stir until well combined. Add gruyère, stir until melted.
Adjust seasoning to taste and serve hot.