Pasta with Walnut Pesto, Sausage, and Broccoli Rabe

Preheat oven to 300 degrees F. Spread walnuts on a baking tray, and toast until golden, 5 to 7 minutes. Cool completely. Combine 1/4 cup nuts, basil, garlic, and 1/4 teaspoon salt in the bowl of a food processor. Process and, while motor is running, drizzle in 1/2 cup olive oil to form pesto; set aside. Chop rest of nuts, and set aside. Bring a large pot of salted water to a boil; cook rigatoni until tender. Meanwhile, heat 2 tablespoons olive oil in a large skillet. When oil is hot, add sausage and cook, breaking up meat, until brown, about 5 minutes. Transfer meat to a small bowl, and leave 1 tablespoon fat in pan. Return skillet to heat, and add rest of olive oil. Add broccoli rabe; cook until just crisp, about 2 minutes. Add 1/4 cup water, cover skillet, reduce heat to medium, and cook until tender, about 5 minutes. Add 1/4 teaspoon salt and 1/8 teaspoon pepper; return sausage to pan to heat through. Toss cooked pasta with pesto; season with salt and pepper to taste. Divide among 4 plates, and top each with sausage and broccoli rabe, a dollop of ricotta cheese, and chopped walnuts.