Ensure your filo pastry is fully defrosted and at room temperature. Preheat your oven to 375°F (190°C) and cover the sheets with a damp towel.

In a large skillet, heat 2 tablespoons of olive oil over medium heat. Add the cabbage wedges and sear for about 5 minutes on each side until golden brown, then slice into ribbons.

In the same skillet, add another tablespoon of olive oil, followed by leeks, potatoes, and carrots. Sauté for around 5 minutes until softened, then add garlic and cabbage, mixing until tender.

Transfer the sautéed mixture to a mixing bowl and add diced corned beef, sea salt, pepper, and dried mustard, combining well.

Brush a 24-cup muffin tin with olive oil to prevent sticking.

Lay down one sheet of filo and brush lightly with olive oil. Stack a second sheet, cut into quarters, and create a cross shape with two pieces. Fill with about 2 tablespoons of the mixture, scrunch the edges to form a parcel, and place into the muffin tin.

Brush the tops lightly with olive oil and bake for approximately 20 minutes until golden brown and crispy.

Cool slightly on a wire rack before serving. Enjoy warm or at room temperature.