Leek & Caramelized Onion Mashed Potatoes

1 1/2 cups onion, thinly sliced

1 large leek, white and light green part only, halved lengthwise and vertically sliced

1 teaspoon sugar

7 tablespoons butter, divided

2 pounds russet potatoes, peeled and cut into 1-inch pieces

2/3 cup half and half

1/2 teaspoon salt

1/4 teaspoon white pepper

1. Melt 2 tablespoons of the butter in a 10-inch nonstick skillet over medium heat. Add the onion, leek, and sugar; cook, stirring occasionally, until golden, about 14-15 minutes. Remove from the heat.
2. Meanwhile, combine the potatoes in a large saucepan with enough cold water to cover by 2-inches. Bring to a boil over medium-high heat. Reduce heat to medium and simmer until potatoes are tender, about 14-15 minutes. Drain; return potatoes to the saucepan.
3. While the potatoes cook, combine the remaining 5 tablespoons butter and half and half in a small saucepan over medium-high heat. Cook until the butter is melted. Pour into the potatoes and mash. Stir in onion mixture, salt, and pepper.