In this puréed vegetable soup, asparagus and leeks are thickened with rice, which adds both body and a slightly nubby texture to the bowl. Little is wasted in the preparation; asparagus ends and leek tops that might otherwise be thrown away are simmered into a delicate broth that serves as the foundation for the other flavors. You can skip the ricotta crostini but some kind of crunchy contrast – plain buttered toast, breadsticks or crackers – makes a nice counterpart on the side.
03In a saucepan, combine leek tops, stock, asparagus bottoms and bay leaf. Simmer for 10 to 20 minutes; strain, discarding the solids and saving the stock.
04Return empty pot to medium-low heat. Add oil, white leek slices and rice. Cook, stirring frequently, until leeks are golden, about 5 minutes. Pour in 1 cup of the stock. Simmer for 10 minutes. Add remaining stock and asparagus middles. Simmer, covered, over low heat, until asparagus is completely tender, 7 to 10 minutes.
05Press soup through a food mill (or purée in a blender, then strain through a coarse mesh sieve; nothing too fine, you want a little texture here). Return soup to pot. Season with salt, pepper and lemon juice to taste. Cover to keep warm.
06Heat oven to 350 degrees. Place bread slices on a baking sheet and toast, turning halfway through, until bread is golden and dry to the touch, about 10 minutes.
07While bread toasts, season ricotta with tarragon, salt and pepper. Rub hot crostini with the cut side of the halved garlic cloves and slather with ricotta. Ladle soup into warm bowls and garnish with the asparagus tips. Serve with crostini.