2 tablespoons (28 g) butter 5 cups (325 g, about 3–4) leeks, white and light green parts only, sliced into 1/4-inch-thick rounds 1⁄2 cup (40 g) panko 1 egg + 1 egg white 2 teaspoons (8 g) salt canola oil, as needed
Add butter to a nonstick skillet over medium heat. Add the leeks. Lower the heat to medium- low and cook until caramelized, about 45 minutes. Remove leeks from pan and set aside.
Mix the panko, egg, egg white, and salt in a small bowl. Mix together with the leeks.d
Add canola oil to a nonstick skillet set over medium heat. Spoon a mound of leek mixture into the pan. Fry until browned, about 2 to 3 minutes per side.
Transfer to a paper towel–lined plate. Serve garnished with sliced green onion and crème fraîche.