As far as I’m concerned, this recipe is worth the price of the book—it’s that good and that easy. You’ve probably spent hours making lasagna, carefully layering in the ingredients, only to find, when you serve it up, that it looks nothing like the perfect squares you envisioned. This version is all about flavor — who cares what it looks like? It requires just one pan and takes about 25 minutes to make, start to finish. Just try it. You’ll never make a traditional lasagna again.
Preheat the oven to 400° F. In a large ovenproof skillet, heat the oil over medium heat until shimmering. Add the beef and cook, breaking up with a wooden spatula, until the meat has browned, 5 to 7 minutes.
Meanwhile, combine the tomatoes, carrots, onion, and garlic in a food processor and chop until coarsely ground but not completely smooth.
When the meat is browned, pour off any accumulated fat. Add the tomato mixture, stock, ricotta, and spinach and combine thoroughly. Bury the lasagna noodles in the sauce, and sprinkle the mozzarella evenly over all.
Bake the lasagna uncovered until the cheese is melted and bubbling, 10 to 15 minutes. Remove the pan from the oven and let stand uncovered for 10 minutes. Serve warm.