Ingredients

• 2 tablespoons unsalted butter

• 1 tablespoon olive oil

• 4 large leeks (about 8 cups), white and light green parts only, halved lengthwise, halves cut into 1/2-inch-thick half-moons

• 4 large celery stalks (about 2 cups), chopped, plus small, tender leaves for garnish

• 6 large Yukon Gold potatoes (about 9 cups), peeled, quartered lengthwise, and cut into 1/2-inch pieces

• 7 cups water

• 2 tablespoons plus 1 teaspoon jarred chicken stock base (such as Better Than Bouillon)

• 1 cup whole milk

• 1/4 cup heavy cream

• 1 1/2 teaspoons kosher salt

• 1/2 teaspoon black pepper

• Dash of freshly grated nutmeg

• Finely chopped fresh chives and crushed potato chips, for garnish