1. Rinse cod under cold water. Place in a large bowl, and cover with cold water. Cover with plastic wrap, and refrigerate 24 hours, changing water every 8 hours.

2. Drain cod. Transfer to a medium saucepan, and cover with water. Add onion and bay leaves. Bring to a boil. Reduce heat, and simmer 10 minutes. Add potato, and cook until cod is easily flaked with a fork and potato is tender, about 20 minutes more. Drain well; discard onion and bay leaves.

3. Preheat oven to 375 degrees. Put cod, potato, 6 tablespoons oil, and the cream into a medium bowl. Mash together with a fork until mixture forms a chunky puree; season with salt and pepper. Cod mixture can be refrigerated in an airtight container up to 2 days.

4. Transfer mixture to a pastry bag fitted with a coupler, and fill each pepper. Transfer to a baking dish large enough to hold peppers in a single layer. Drizzle with remaining 2 tablespoons oil, and sprinkle with garlic slices. Cover with foil, and bake until heated through, about 20 minutes. Serve immediately, drizzled with oil if desired.