01 -  Preheat oven to 375°F (190°C). Lightly grease four large oven-safe soup bowls or ramekins. 
 02 -  Heat olive oil in a medium saucepan over moderate heat. Sauté onion and garlic until translucent, approximately 3 minutes. Stir in tomato passata, oregano, salt, and black pepper. Simmer gently for 10 minutes and set aside. 
 03 -  In another saucepan, melt butter over medium heat. Whisk in flour and cook for 1 minute, stirring continuously. Gradually pour in milk, whisking until the mixture thickens, about 3–4 minutes. Remove from heat. Stir in grated Parmesan, Gruyère, ground nutmeg, salt, and pepper. Let cool slightly, then whisk in egg yolks one at a time. 
 04 -  In a clean mixing bowl, beat egg whites (with cream of tartar, if desired) using an electric mixer or hand whisk until stiff peaks form. Carefully fold the whipped whites into the cheese mixture in two to three increments to maintain the airy texture. 
 05 -  Spoon a thin layer of prepared tomato sauce into each bowl. Place a piece of lasagne sheet (break if necessary to fit), top with additional sauce, a generous tablespoon of ricotta, and a sprinkle of mozzarella. Continue layering until bowls are almost full, finishing with sauce on top. 
 06 -  Distribute the cheese soufflé mixture evenly over the layered bowls, smoothing the surface gently. 
 07 -  Arrange bowls on a baking tray and bake for 30–35 minutes until the soufflé tops are puffed and golden brown. 
 08 -  Allow to cool for 5 minutes. Garnish each bowl with fresh basil leaves and serve immediately.