2 tablespoons olive oil
1 fennel bulb, cored and sliced thinly
1 large leek, cleaned and sliced into 1/2-inch pieces
Salt & freshly ground black pepper
1 teaspoon lemon zest
1 tablespoon butter

Heat oil in a medium sized skillet over medium heat; add fennel and cook, stirring occasionally until translucent, about 10 minutes.

Add leeks, season with salt and pepper, cook 5 minutes more.

Stir in lemon zest and butter, adjust seasonings, serve.

from food.com