Preheat the oven to 220C/400F/Gas 6. Grease an ovenproof dish with butter.
Boil the eggs for 8-10 minutes in a large pan of boiling water. Remove from the pan using a slotted spoon and run under cold water until cool enough to handle.
When cool, peel the eggs and slice into rings. Set aside.
For the mashed potatoes, cook the potatoes in a separate pan of boiling, salted water for 10-15 minutes, or until tender. Drain well.
Pass the potatoes through a ricer until smooth, collecting the mash in a clean pan. Heat the mashed potatoes over a low heat and add the butter and cream, mixing until well combined. Season, to taste, with salt and freshly ground white pepper. Set aside and keep warm.
Meanwhile, boil the leeks in a pan of boiling water for 3-4 minutes, or until tender, then drain well. Stir the cooked leeks into the mashed potatoes until well combined.
For the sauce, melt the butter in a pan over a low heat. Whisk in the flour until the mixture is thick and well combined.
Gradually add the milk, whisking continuously, for 4-5 minutes, or until all of the milk has been incorporated into the mixture and the sauce is thick and smooth.
Add the mustard powder and season, to taste, with salt and freshly ground black pepper.
Stir in the cheeses until melted.
For the topping, in a large bowl, mix together all of the topping ingredients until well combined. Set aside.
Spoon the mashed potatoes and leeks into the bottom of the prepared ovenproof dish, pressing down to form an even layer.
Arrange the slices of boiled egg on top in a circular pattern, overlapping them until all of the mashed potatoes are covered.
Season, to taste, with salt and freshly ground black pepper, then pour over the cheese sauce. Sprinkle over the topping.
Place the dish onto a baking tray to catch any drips. Transfer the dish to the oven and bake for 20-25 minutes, or until the topping is crisp and golden-brown and the sauce is bubbling.
Meanwhile, heat a little oil in a non-stick frying pan over a medium to high heat. Add the bacon chops and fry for 3-4 minutes on each side, or until crisp on both sides and completely cooked through (the juices will run clear when the meat is pierced in the thickest part with a skewer).
To serve, spoon a portion of the Anglesey eggs into the centre of four serving plates. Place one bacon chop alongside each. Garnish with the flatleaf parsley.