Lightly spoon flour into dry measuring cups; level with a knife. Combine flour and next 4 ingredients (through salt) in a large bowl, stirring with a whisk. Set aside.
Heat the olive oil in a small skillet over medium-high heat. Add sliced leek; sauté 3 minutes or until leek is tender and lightly browned. Stir the leek mixture into the flour mixture. Combine reduced-fat milk, butter, and egg; add the milk mixture to flour mixture, stirring until smooth.
Pour about 1/4 cup batter per pancake onto a hot nonstick griddle or nonstick skillet. Cook 3 minutes or until tops are covered with bubbles and edges look cooked. Carefully turn pancakes over; cook 2 minutes or until bottoms are lightly browned.