In a large casserole, heat the olive oil over medium-high heat. Add the diced smoked streaky bacon and cook for 6-8 minutes until it becomes crispy and has released its fat. Use a slotted spoon to remove the bacon, leaving the fat in the pan.

Next, add the beef and pork mince to the pan and cook until browned. Stir in the chopped onions, carrots, celery, and minced garlic, cooking until the vegetables soften.

Add the tomato purée, brown ale, plum tomatoes, beef stock, Worcestershire sauce, and the beef stock pot. Season with dried thyme, bay leaf, sugar, sea salt, and cracked black pepper. Bring the mixture to a simmer and let it cook for about 30 minutes, stirring occasionally.

While the meat sauce is simmering, prepare the béchamel sauce. In a separate saucepan, melt the butter over medium heat. Stir in the plain flour and cook for a minute to form a roux.

Gradually whisk in the whole milk and continue to stir until the sauce thickens. Add the double cream, English mustard, mature Cheddar, ground nutmeg, sea salt, and white pepper. Mix until the cheese has melted and the sauce is smooth.

For the potato topping, peel and slice the Maris Piper potatoes thinly. In a bowl, toss the potato slices with olive oil, butter, egg yolk, sea salt, and white pepper.

To assemble the lasagna, spread a layer of the meat sauce in a baking dish, followed by a layer of dried lasagna sheets. Pour some béchamel sauce over the sheets, then repeat the layers until all ingredients are used, finishing with a layer of béchamel sauce on top.

Arrange the sliced potatoes over the top layer of béchamel, overlapping them slightly. Sprinkle the remaining mature Cheddar on top.

Bake in a preheated oven at 180°C (350°F) for about 45-50 minutes, or until the potatoes are golden and cooked through.