This lively springtime pasta dish was inspired by a recipe from “River Cafe London,” the most recent cookbook from Britain's landmark restaurant. The asparagus is finely chopped in the food processor; half is sautéed until tender and half is kept al dente for pleasing contrast in texture. A cup of cream binds the asparagus into a silky sauce just thick enough to coat the pasta while a sprinkle of lemon zest and a squeeze of lemon juice at the table brighten up the flavors.