Lay down about 6 feet (1.8 meters) of tinfoil on a flat surface. Place place 4 clusters of 2 lasagna noodles towards the left half of the foil sheet, leaving about a ½-inch (1 cm) gap in between each cluster.
Fold the right half of foil over the noodles, pressing flat. To help you see where the noodles are, run your finger along the edges of the noodles to create a rough outline in the foil.
Fold the top and bottom flaps of foil over, creasing and pressing flat.
Flip the foil sheet onto the table so that it’s now standing, then arrange into a square box, using the 4 groups of noodles as a visual guide. Fold and crease over any excess foil to join the ends together, then set aside.
In a large pot, melt the butter over medium heat.
Whisk in the flour, cooking until the mixture reaches a light golden color.
Slowly drizzle in the milk and bring to a boil, whisking constantly until smooth. Mix in salt, pepper, and nutmeg. Bring to a boil.
Transfer the béchamel to a large bowl and press plastic wrap onto the surface of the sauce to prevent a skin from forming. Set aside.
Heat oil in a very large pot over high heat. Once the oil begins to shimmer, add the onions, carrots, and celery and cook until the vegetables have started to sweat but aren’t browning.
Add in the ground beef and use a wooden spoon or spatula to break up the meat into small pieces.
Cook the beef, stirring occasionally, until half of the liquid has evaporated.
Add in the tomato sauce, tomato paste, chicken stock, salt, and pepper, stirring to combine evenly and breaking up any last lumps.
Turn down the heat to low, and simmer, covered, for about 2 hours.
Preheat oven to 350°F (180°C).
To assemble, line a greased 9x9-inch (23x23-cm) square baking pan with 2 sheets of foil that extend over the sides.
Spread a thin layer of béchamel on the lined baking pan and top with 2 lasagna noodles. Spread a thin layer of meat sauce evenly across the noodles, followed by a thin layer of béchamel. Repeat the layering process, following the order of: 2 noodles, meat sauce, and béchamel. Alternate the direction of the lasagna sheets after every layer.
After 50 layers, place the foil box over the lasagna, helping it stay upright and stable.
Continue with the layering process until the 99th layer.
Sprinkle Parmesan on top, then cover the whole lasagna with foil.
Bake for about 1½ hours, uncovering the foil halfway, until the top is a deep golden brown.
Cool for at least 2 hours, then carefully lift out the lasagna with the foil sleeves onto a large cutting board.
Peel away the foil walls, then sprinkle the top of the lasagna generously with chives.