Moules Frites

Place a large rimmed baking sheet in oven; preheat to 425°F. Bring a kettle of water to a boil.

Place potato wedges in a medium bowl and cover with boiling water. Let stand for 5 minutes. Drain and pat dry. Toss with 1 tablespoon oil, 1/4 teaspoon ground pepper, salt and cayenne in the medium bowl. Spread the wedges in a single layer on the preheated pan. Bake, flipping once, until golden and crispy, 25 to 30 minutes.

Meanwhile, whisk egg yolk, 1 teaspoon parsley, lemon juice, 1/2 teaspoon shallot, mustard and the remaining 1/4 teaspoon pepper in a small bowl. While whisking, drizzle in 2 tablespoons oil until blended. Set aside.

Heat the remaining 1 tablespoon oil in a large pot over medium heat. Add leek and the remaining 1 tablespoon shallot; cook, stirring occasionally, until softened, about 5 minutes. Add mussels, wine and the remaining 1 tablespoon parsley. Cover and steam until the mussels open, 3 to 5 minutes. (Discard any that don't open.)

Transfer the mussels to a large serving bowl and top with scallions and crushed red pepper, if desired. Serve the mussels and potato wedges with the aioli for dipping.