Step 1Butter 6 (4-ounce) ramekins and place in the refrigerator. When the butter hardens, add a second coating of butter to the ramekins. Set aside. Heat the oven to 350 degrees.
Step 2Heat the olive oil in a medium skillet over low heat. Add the leeks, shallots and salt and cook until the leeks are translucent but still retain a bite, about 10 minutes. Drain.
Step 3Place the whipping cream and half-and-half in a medium saucepan and bring to a boil. Turn off the heat and cool.
Step 4Put the leek mixture in the blender along with the cream mixture and the egg whites. Blend until smooth, about 30 seconds.
Step 5Spoon the mixture into the prepared ramekins. Place the ramekins in a large baking pan. Pour boiling water into the pan until it reaches halfway up the sides of the ramekins. Place the pan in the oven. Bake until the flans are set, about 35 to 40 minutes.
Step 6To serve, unmold the flans and garnish with 2 (3-inch) pieces of chives crossed over the top.