Heat the olive oil in a large pot over medium-high heat. Add the minced garlic and chopped onion, cooking for about 2 minutes until fragrant and translucent. If using, add the finely diced celery and carrot, cooking for an additional 3 minutes.

Turn the heat to high and add the ground beef. Break it up with a spoon as it cooks, browning it evenly. After the beef is browned, pour in the red wine, letting it simmer for about 2 minutes.

Add the crushed tomatoes, tomato paste, crumbled bouillon cubes, Worcestershire sauce, bay leaves, and thyme to the pot. Season with salt and pepper, stirring well to combine. Bring the mixture to a simmer, then cover and let it cook for at least 45 minutes.

Meanwhile, cook the spaghetti according to the package directions, but reduce the cooking time by 1 minute. Drain the spaghetti and return it to the pot.

Mix about half of the Bolognese sauce with the cooked spaghetti in the pot. Make sure the pasta is well-coated with the sauce.

Preheat your oven to 180C/350F. In a casserole dish, spread half of the pasta mixture evenly across the bottom. Top with half of the remaining Bolognese sauce and layer with Swiss cheese slices.

Add the remaining spaghetti mixture on top, covering it with the rest of the Bolognese sauce. Finish with a generous amount of shredded mozzarella cheese on top.

Cover the dish loosely with foil and bake in the oven for 25 minutes. After that, remove the foil and bake for another 10 minutes until the cheese is bubbly and golden.

Once baked, let the dish stand for about 10-15 minutes before slicing and serving. This allows the layers to set, making it easier to serve.