Preheat oven to 425°F.

Preheat a large saucepan over medium heat. Add the bacon lardon, cooking until bacon fat has rendered and bacon is golden and crisped. Stir occasionally to prevent burning. Remove bacon, and pour off bacon fat until roughly two tablespoons remains in the pan. Reserve the remainder bacon fat.

Add onion and fry, stirring frequently, until caramelized. Remove onion from pan, reserving separately.

Add remainder of bacon fat and carrot slices and fry briefly, until carrots begin to sweat and cook through. Remove and reserve separately.

Add a tablespoon of vegetable oil if necessary, then add pork sausages, frying until lightly golden, about 2 minutes each side. Reduce heat to medium, and add beer to the pan to cover sausages about halfway. Cook until finished, flipping halfway through (about 5 minutes). Set sausages aside, slicing them thinly when they cool enough to touch.

Add chicken stock to the pan, then bring heat to high and reduce the liquid by half. Scrape the bottom of the pan with a wooden spoon to loosen any fond.

In a separate casserole dish, layer a third of the potato slices on the bottom of the dish, then lightly season with salt and pepper. Add a layer of bacon, then onion, then carrot, then a third of the pork. Repeat once more, then top with the remainder of the potato. Season each layer as you go (salting lightly if you’re using presalted stock).

Cover with aluminum foil, then a casserole lid, and place in the oven for 40-45 minutes. Check towards the end of the cooking time to ensure the liquid hasn’t completely evaporated. Add water or additional stock if desired.