In a medium bowl, stir together the ricotta and Parmesan cheeses. Season the cheeses with salt and pepper; stir in the egg.
In another medium bowl, stir together the spinach and pesto.
Spray a glass baking dish with nonstick spray. Spread 1 cup of the pasta sauce in the prepared dish. Arrange 3 noodles side-by-side atop the sauce. Spread 1¼ cups of the ricotta cheese mixture over the noodles in a thin layer. Drop ⅓ of the spinach mixture over the cheese by spoonfuls. Repeat the layering with sauce, noodles, ricotta cheese mixture and spinach mixture 2 more times. Top with the remaining 3 noodles and 1 cup of sauce.
Preheat the oven to 350°F. Cover the lasagna with foil..
Bake for 35 minutes. Uncover; sprinkle with the fontina cheese. Bake the lasagna until heated through, the sauce is bubbling and the cheese on top is melted, about 15 minutes longer. Let stand for about 10 minutes before serving
Notes
The original recipe called for using no-boil lasagna noodles. This, of course, makes this recipe even quicker. I haven't had a whole lot of luck in the past with the no-boil noodles, but I encourage you to try them in this recipe.