Start by peeling and chopping the potatoes into even pieces. Place them in a large pot of salted water. Boil for about 15 minutes until soft. You should be able to mash them easily with a fork.

Drain the potatoes well and return them to the pot. Add butter, warm milk, salt, and pepper. Mash until smooth and creamy. Do not leave lumps unless you prefer a chunky texture.

Add chopped onion, garlic and mustard powder to the mashed potatoes. Mix well so the flavors spread evenly. The onion adds sweetness, while garlic gives a rich taste.

Add most of the grated cheddar cheese into the potato mixture. Save a little for topping later. Stir until the cheese melts slightly into the warm potatoes.

Grease an oven-safe baking dish with a little butter. Spoon the potato mixture into the dish. Spread it evenly using a spatula for a smooth surface.

Sprinkle the remaining cheese over the top. Add breadcrumbs for a crispy golden layer. This will create a nice crunchy texture after baking.

Preheat the oven to 180°C (350°F). Place the dish in the oven and bake for 30–35 minutes. The top should turn golden and slightly crispy.

Remove the pie from the oven and let it cool for a few minutes. Serve warm with vegetables or salad. Enjoy the creamy inside and crispy top.