Make sure to use skin-on salt cod; the natural gelatin in the skin is vital to emulsifying the sauce.
- 4 (4-by-4–inch) skin-on boneless salt cod filerts (about 1 1/2 lbs.)
- 1 cup extra-virgin olive oil
- 5 cloves garlic, thinly sliced
- Put salt cod filets into a large bowl. Cover cod with water, refrigerate, and soak, changing water 6–8 times, for 48–72 hours. Remove cod from water; pat dry.
- Heat oil in a large skillet over medium-low heat. Add sliced garlic; cook, stirring, until garlic is light golden brown, 4–5 minutes. Using a slotted spoon, transfer garlic to a plate; set aside.
- Reduce heat under skillet to very low; let cool for 5 minutes. Add cod filets, skin side up, and cook until just hot, spooning the hot oil over them, 8–10 minutes. Carefully transfer all but a few tablespoons of the oil to a small pot over very low heat. Flip cod filets; arrange toward center of skillet. Allow cod to cook gently until bubbles of gelatin begin to form in oil.
- Gently rock skillet back and forth every 1–2 minutes while whisking oil in skillet constantly to form an emulsion. As more gelatin forms in skillet, slowly drizzle in reserved oil a few tablespoons at a time, while whisking constantly, to make a smooth sauce, about 20 minutes in all. Garnish with reserved garlic.