2 pounds baby Yukon Gold or Red Bliss potatoes (20 to 25 potatoes, 1 1/2 to 1 3/4 inches in diameter)
1 sprig fresh rosemary
2 cups homemade or low salt chicken broth
2 tablespoons good quality extra virgin olive oil
1 tablespoon unsalted butter
1 teaspoon kosher salt (less if broth is salty
1 to 2 tablespoons thinly sliced fresh chives
fleur de sel or other sea salt for serving - optional.