1 pound salt cod, desalted
2 medium onions, quartered
7 large cloves garlic (3 halved, 4 minced)
2 bay leaves
12 ounces potatoes
2/3 cup milk
3/4 cup extra virgin olive oil
3/4 teaspoon coarse salt ground black pepper to taste
Heat the oven to 375 degrees.
Oil a small (4 cup) gratin dish. In a saucepan, combine 2 quarts water with the onions, the halved garlic and bay leaves. Bring to a boil, reduce to a simmer, add the salt cod, and cover the pot tightly. Turn off the heat and let the fish sit in the water 10 to 15 minutes. Remove from the water and set aside the water for cooking the potatoes. When the fish is cool enough to handle, pick out any bones and remove any skin. Flake the fish. Transfer to a food processor.
Simmer the potatoes until very tender. Drain the potatoes and mash. Add 1/3 cup of the milk and 1/4 cup of the olive oil to the potatoes and combine well. In a saucepan, heat another 1/4 cup of the olive oil over medium-low heat and add the minced garlic. When garlic begins to sizzle, remove pan from heat. Add the garlic and oil, along with the the salt, to the salt cod in the processor.
Combine the remaining 1/3 cup of milk and 1/4 cup oil and add to processor in slow stream. Continue to process until fluffy.
Add the salt cod purée to to the potato mixture and combine well. Season with pepper.
Spoon the mixture into the gratin dish, drizzle with 1 to 2 tablespoons olive oil, and bake until the top begins to brown. Serve hot.