In a large pot, add in 1 tablespoon of vegetable oil and place on medium heat. Once hot, add in the onions, garlic, celery, and carrot. Fry for 10 minutes, stirring frequently, until the onions have softened.
Add the lardons (bacon) and sausages to the pan. Break apart the sausages until ground or minced. Season with dried sage, paprika, a pinch of flaky salt and ground black pepper. Fry off and stir for another 10 minutes.
Once the meat has browned slightly in the pan, sprinkle in 1 tablespoon of plain flour and stir, then add in the chicken stock and stir to combine. Bring to the boil, then leave to simmer while you make the béchamel sauce until the sauce has thickened slightly. Taste and season accordingly once cooked.
Preheat the oven to 180c fan / 385F. Place a medium-sized saucepan on medium heat. Add in the butter and once melted, add in the plain flour. Stir with a hand whisk until a paste has formed. Then pour in 100-200ml of the milk, leave to settle, then whisk until smooth and thickened. Pour in 200ml more of milk and once again, let the milk heat up, then whisk until combined and smooth. Repeat this until the milk has run out and you have a smooth, slightly thick, silky bechamel sauce. Next, season with ground black pepper, ground nutmeg, and cheddar cheese. Whisk until smooth. Taste and season accordingly.
Get yourself a lasagne dish or deep tray that serves around 6 people (9x11 inches). Begin with a thin layer of the meat sauce. Follow with lasagna sheets (try not to overlap the sheets - cover the whole tray/dish). Top with a layer of meat sauce, bechamel sauce, and grated mozzarella cheese. Then repeat with a layer of pasta sheets, meat sauce, bechamel sauce, and grated mozzarella cheese. Repeat again and again.
To finish, lay down a final layer of pasta sheets, then generously coat the top with grated mozzarella cheese and grated parmesan cheese. Cover with aluminium/tinned foil and place in the oven for 35 minutes, then remove the tinned foil and place in the oven for another 10 minutes for that golden top.
Remove the Christmas lasagna from the oven and serve!!! Enjoy, my friends!