For the Bolognese ragu: Preheat the oven to 300 degrees F. Smear 1 tablespoon butter in an even layer over the bottom and sides of a Dutch oven. Set aside.
In a large skillet over medium heat, render the bacon until cooked through but not crisp, 5 to 7 minutes. Transfer the bacon to a paper towel and pour off all but 1 tablespoon of the bacon fat from the skillet. Add the remaining 1 tablespoon butter and melt over medium heat. Add the garlic, celery, carrots and onion and saute until the onion is translucent and the vegetables are softened, about 8 minutes. Transfer the vegetables to the Dutch oven.
Add the oil to the skillet and add the beef. Cook the meat, breaking it apart with a wooden spoon, until uniformly brown, about 15 minutes. Transfer the beef and bacon to the Dutch oven and pour in the chicken stock, wine and tomato puree. Transfer to the oven and cook, stirring occasionally, for 3 to 4 hours.
If there is a large amount of fat on top of the sauce, skim it off with a large spoon. Stir in the cream and Parmigiano-Reggiano. Taste for seasoning, adding salt and pepper if needed.
For the cheese sauce: In a large saucepan, melt the butter over medium heat. Add the flour, whisking for a minute. Add the milk and cream and cook, whisking, until the mixture thickens, 5 to 10 minutes. (The process goes more quickly if you warm the milk and cream beforehand.) Add salt and pepper to taste. Remove from the heat, add the fontina and nutmeg and whisk to combine.
For the lasagna: Preheat the oven to 375 degrees F. Butter a 9-by-13-inch baking dish along the bottom and sides.
Spread a thin layer of the ragu sauce on the bottom of the baking dish and top with a single layer of noodles. Top with another layer of the ragu sauce. Spoon a thin layer of the cheese sauce over the ragu in the baking dish. Top with a second layer of noodles and continue layering with the ragu, cheese sauce and noodles until you've finished the noodles and reached the top. Finish with a last layer of ragu and cheese sauce and top with the Parmigiano-Reggiano. Bake until bubbling, 30 to 35 minutes.
This is a slow-cook ragu. You can make it in a slow cooker, though I prefer to do it in a Dutch oven in a 300 degree F oven. You can make it a few days ahead and keep it covered in the refrigerator. The cheese sauce can be made a day ahead and refrigerated.