Place the sardine fillet, minced garlic, mayonnaise, Dijon mustard, grated Parmesan cheese, and lemon juice into a food processor.
Pulse the ingredients until the sardine is finely chopped, and the mixture is well combined.
Season the mixture with salt and black pepper according to your taste.
With the food processor running, slowly drizzle in the extra-virgin olive oil until the dressing reaches a smooth and creamy consistency.
Stop the food processor and scrape down the sides to ensure all ingredients are well incorporated.
Taste the dressing and adjust the seasoning if needed.
Transfer the dressing to a bowl and refrigerate for at least 30 minutes before serving to allow the flavors to meld.