To begin, make sure the salt cod has been properly soaked to remove excess salt. Rinse the cod pieces under cold water and pat them dry with paper towels. This step is crucial for achieving the right level of saltiness and texture in the final dish.

In a large skillet or shallow pan, heat the olive oil over low to medium heat. Add the sliced garlic and dried chili pepper, if using. Cook gently for 2-3 minutes, stirring occasionally, until the garlic is just golden but not browned. This will infuse the oil with a deep garlic flavour.

Remove the garlic and chili from the oil using a slotted spoon and set aside. The infused oil will be used for the cod, while the garlic and chili will later be added back for extra flavour and garnish.

Lower the heat to medium-low and add the cod pieces to the skillet, skin side down. Allow the cod to cook slowly, without stirring, for about 8-10 minutes. As it cooks, the cod will release its natural gelatine, which is essential for creating the signature "pil pil" emulsion.

Carefully tilt the skillet to one side and, using a fine mesh strainer or small spoon, begin to gently stir the oil and gelatine mixture in a circular motion. This helps to form a thick, glossy sauce as the natural gelatine emulsifies with the olive oil. Continue this process for about 5-7 minutes.

Flip the cod pieces over and continue gently stirring the sauce for another 5 minutes, ensuring that the cod is cooked through and the sauce has a smooth, creamy consistency. Adjust the heat if necessary to prevent the sauce from breaking.

Return the garlic and chili to the skillet, stirring them into the sauce. This will add a final burst of flavour to the dish. Let the mixture cook for 2 more minutes to fully blend the flavours.

Serve the Bacalao al Pil Pil directly from the skillet or transfer to a warm serving dish. Garnish with freshly chopped parsley and pair with crusty bread to soak up the luscious sauce. For an authentic touch, consider serving alongside roasted piquillo peppers or a green salad.