Rich and nutty pistachios are ground alongside fennel, basil, and tarragon to make this delicious herbal pesto, which is then mixed with ricotta and layered with lasagna noodles and lots and lots of Parmesan and white cheddar.
For the pesto, in a blender or food processor, combine the fennel, pistachios, basil, tarragon, salt, and pepper and blend until smooth. With the motor running, slowly add the oil in a thin, steady stream through the hole in the cap or feed tube. Blend for 10 seconds more, or until thick and smooth. Cover and set aside.
Preheat the oven to 375°F (190°C).
For the lasagna, bring a large pot of water to a boil. Place the lasagna noodles in the water, working in batches as necessary, and cook until slightly bendable, 4 to 5 minutes. Remove with tongs and transfer to a colander to drain.
In a medium bowl, mix the pesto, ricotta, and cream together until combined.
Place 3 or 4 of the noodles in the bottom of a 9 by 13-inch (23 by 33-cm) rectangular casserole dish, keeping them in a flat, even layer. Take 1 cup (100 g) of the Parmesan and set it aside for later use. Spread one-third of the ricotta mixture over the noodles, then sprinkle with one-third of the Parmesan. Place 3 or 4 noodles in an even layer on top of the Parmesan and repeat two more times, so you have three layers of the ricotta mixture and are left with the noodles on top.
Sprinkle the cheddar and reserved Parmesan evenly over the top. Place the casserole dish on a baking sheet and place it in the oven. Bake until the cheese is bubbling around the edges, about 35 minutes. Allow to cool for 15 minutes before slicing and serving.