Boil the 4 large eggs: Carefully place eggs in a pot of boiling water and cook for 6-7 minutes for a slightly runny yolk, or 8-9 minutes for a firmer yolk. Immediately transfer to an ice bath to stop cooking and chill completely. Once cold, gently peel the eggs.

Prepare the sausage mixture: In a bowl, combine the sausage meat, Dijon mustard, chopped parsley, chopped sage (if using), salt, and pepper. Mix well until everything is evenly distributed.

Assemble the Scotch Eggs: Divide the sausage mixture into 4 equal portions. Flatten one portion into a thin patty on a piece of plastic wrap. Place a peeled egg in the center of the patty. Carefully wrap the sausage meat around the egg, ensuring it's completely sealed with no cracks. Repeat with the remaining eggs and sausage.

Set up the dredging station: Prepare three shallow dishes. Put flour in the first, beaten eggs in the second, and panko breadcrumbs in the third.

Coat the eggs: Roll each sausage-wrapped egg first in the flour, shaking off any excess. Then dip it in the beaten egg, allowing any extra to drip off. Finally, roll it thoroughly in the panko breadcrumbs, pressing gently to ensure a thick, even coating.

Cook the Scotch Eggs (Deep Fryer Method): Heat the vegetable oil in a deep pot or Dutch oven to 325-350°F (160-175°C). Carefully lower the Scotch eggs into the hot oil, cooking 1-2 at a time to avoid overcrowding. Fry for 5-7 minutes, turning occasionally, until golden brown and the sausage meat is cooked through.

Cook the Scotch Eggs (Air Fryer Method): Preheat your air fryer to 375°F (190°C). Lightly spray the coated Scotch eggs with cooking oil. Place them in the air fryer basket in a single layer, ensuring they don't touch. Cook for 12-15 minutes, flipping halfway through, until golden brown and the sausage meat is cooked.

Serve: Remove the Scotch eggs from the oil or air fryer and place them on a wire rack lined with paper towels to drain any excess oil. Serve warm or cold, cut in half, perhaps with a dollop of mustard or chutney.