1. Place potatoes in a saucepan. Add water to cover potatoes; bring to a boil. Reduce heat to medium. Simmer 10 minutes; drain potatoes. Set aside.
2. Preheat broiler to high.
3. Heat a large Dutch oven over high heat. Add oil to pan; swirl. Add fish, skin side down; cook 2 minutes or until skin is crisp. Remove from pan; break into 2-inch pieces.
4. Reduce heat to medium-high. Add leek and sliced garlic; sauté 5 minutes or until lightly browned, stirring occasionally. Add wine; bring to a boil, scraping pan to loosen browned bits. Add 1 cup water and next 6 ingredients (though bay leaf); bring to a boil. Add potatoes, fish, and mussels; cover and cook 4 minutes or until shells open and fish is done. Discard any unopened shells, thyme, and bay leaf. Sprinkle with parsley.
5. Arrange bread in a single layer on a baking sheet. Broil 1 1/2 minutes or until toasted. Rub bread generously with cut side of garlic. Serve with stew.