The simplicity of this pasta dish belies its deliciousness and elegance. Radicchio, a member of the chicory family, is much loved in Venice, Italy, where home cook Francesco Bernardi taught us his recipe. Chopped radicchio is browned in garlic-infused olive oil, its flavor becoming rich and complex and its texture softening slightly. The layers of pleasantly bitter notes—from the radicchio and the toasted walnuts—are perfectly balanced by the nuttiness and umami of Parmesan, the bright tang of lemon juice and the pungency of black pepper.