Trim membranes and tough veins from the beef liver, then soak the pieces in milk for thirty minutes before draining and patting them completely dry.
Sauté finely chopped onion in butter until translucent, add garlic and diced liver, and cook until the liver reaches 71 degrees Celsius at the center.
Cool the cooked liver briefly and chop everything very finely, then combine with mashed potatoes, cornmeal, parsley, salt, and black pepper in a wide bowl.
Beat the egg and incorporate it into the mixture, stirring until thick enough to shape; chill for twenty minutes if the filling seems excessively soft.
Shape the mixture into small cylinders with damp hands, roll evenly in breadcrumbs, and rest on parchment while heating neutral oil to 175 degrees Celsius carefully.
Fry in small batches until the coating turns golden and crunchy, drain on a rack, and allow the centers to cool slightly before serving warm.
