Preheat your oven to 180°C
Peel and chop the potatoes into chunks. Place them in a large pot of salted water and bring to a boil. Cook until the potatoes are tender when pierced with a fork, usually around 15-20 minutes.
Heat the olive oil in a large pan on a medium heat. Add the chopped onion, diced carrot, and diced celery. Sauté for 5 minutes until the vegetables begin to soften. Add the minced garlic and cook for an additional minute until fragrant.
Add the beef mince to the pan. Cook, stirring frequently, until the meat is browned and cooked through. Stir in the tomato paste and cook for another minute.
Add the beef stock, worcestershire sauce, instant gravy mix, bay leaf, salt, and pepper to the pan. Stir well to combine all the ingredients. Reduce the heat to low and let the mixture simmer for 8 - 10 minutes. Remove the bay leaf before assembling the pie.
Drain the cooked potatoes and return them to the pot. Add the butter, milk, salt, and pepper. Mash the potatoes until smooth and creamy.
Transfer the cooked beef mixture to a large baking dish and spread it out evenly. Spoon the mashed potatoes on top of the meat mixture, spreading them out to cover the entire surface. Use a fork to create a decorative pattern on the potatoes.
Sprinkle the shredded cheddar cheese over the mashed potatoes, covering them evenly. Place the cottage pie in the preheated oven and bake for 25-30 minutes, or until the mashed potatoes turn golden brown and the filling is bubbling around the edges.
Remove from the oven and let it cool for a few minutes. Garnish with fresh parsley, if desired, before serving.