Serve it on a rimmed plate.
1. Preheat oven to 350°.
2. Melt butter in a large nonstick skillet over medium heat. Add leek; sauté 6 minutes.
3. Press broccoli between several layers of paper towels to remove excess moisture. Combine milk and next 5 ingredients, stirring with a whisk. Add leek mixture, broccoli, potato, and 1/3 cup cheese. Pour into a 9 1/2-inch-deep dish pie plate coated with cooking spray. Sprinkle with remaining 1/3 cup cheese and breadcrumbs. Bake at 350° for 25 minutes or until center is set.
4. Preheat broiler.
5. Place frittata on center rack of oven; broil 4 minutes or until golden brown. Remove from oven; let stand 5 minutes. Cut into wedges.