With the required ingredients in your inventory, head to the Prep Kitchen (once unlocked via game progression) and tap the tab with the golden Wishelin serving tray on it (Signature Dish tab) and prep the desired dish accordingly if you have all required Ingredients.

Once prepped, it's time to either wait for the Wishelin Inspector to visit the venue the Signature Dish is prepped for - or you can CALL him at the expense of a bit of gold.

Successfully serving the Wishelin Inspector earns you a Wishelin Star!!