This soup comes from the cold northern plains of Picardy, though you will find it all over France. A bit of bacon provides meaty backing to the hearty purée of peas. In the days when pea soup was the entire meal, the purée would be stiff, known in England as pease pudding. This version is pourable.
Rinse the peas well, then put in a bowl, add water to cover, and let soak for 1 hour. Drain the peas, put them in a soup pot, and add the water, bacon, thyme, and pepper. Cover, bring to a boil, reduce the heat to very low, and simmer until the peas are very tender and falling apart, 1¼ to 1½ hours. Add salt halfway through cooking, with more water if the pan seems dry. When the peas are done, most of the water should be absorbed and the peas should be soupy. If necessary, remove the lid toward the end of cooking so some of the water evaporates. Meanwhile, make the croutons.
Remove the piece of bacon from the soup and set it aside; discard the thyme sprigs. Work the soup through a food mill, or purée it in a food processor and then work it through a strainer to remove any fibers. Return the soup to the pot. Dice the bacon, discarding any rind or bits of cartilage, and add it to the soup. It may be refrigerated for up to 3 days, or frozen for 3 months.
To finish, bring the soup back to a boil. If it is very thick, add enough water so it pours easily from the spoon. It should still be thick and rich. Taste and adjust the seasoning. Stir in the butter until almost melted, and pour the soup into a tureen or spoon it into bowls. Sprinkle the croutons on top and serve.
© 2007 All rights reserved. Published by Chronicle Books.