How to Make It
Preheat the oven to 350°. In a large saucepan, melt the 1 tablespoon of butter in the olive oil. Add the Serrano ham, onion, leek and carrot and cook over moderate heat, stirring occasionally, until softened, about 8 minutes. Add the stock and lentils and bring to a boil over moderately high heat. Simmer the soup over low heat, stirring occasionally, until the lentils are tender, about 45 minutes.
Meanwhile, on a baking sheet, toss the diced bread with the melted butter and bake for 8 minutes, or until browned.
Puree the soup in a blender in batches; transfer the puree to a clean saucepan. Add the cream, bring to a simmer and season with salt and pepper. Serve the soup in bowls, garnished with the croutons.