Although rarely served in fine restaurants and almost never appearing on smorgasbords, soups are essential in traditional Swedish cuisine. One soup in particularrtsoppahas a distinguished history.

Yellow pea soup has sustained the working class since the age of the Vikings. When Catholicism was the reigning religion of Sweden, rtsoppa, which is studded with salt pork, became the meal of choice before Sabbath every week.

Today, although the Catholic Church has few followers in predominantly secular Sweden, the soup is still eaten every Thursday in many households. rtsoppa is always served with mustard; you either swirl a bit of mustard into the soup to season the whole lot or dip the tip of your soupspoon into the spicy condiment before every bite.

Yellow Pea Soup (rtsoppa)

Serves 4 to 6

1 pound whole dried yellow peas (split peas are acceptable)
2 onions, chopped fine
1 whole onion, peeled, halved, and each half stuck with 1 whole clove
1/2 pound piece lean salt pork
1/4 teaspoon marjoram
1/2 teaspoon thyme
Salt (if needed)
Whole-grain brown mustard

1. Soak the peas in water at least 12 hours.

2. Drain the peas, put them in a large saucepan, cover with 6 cups cold water, chopped onions, and the onion halves with cloves. Bring to a boil, then reduce heat to a medium simmer. Add the salt pork, cover, and let simmer for about 90 minutes, skimming off any foam that rises to the surface. Add the marjoram and thyme to the pan, stir, and let simmer another 15 minutes. Season to taste with salt. Remove the pork, allow to cool just until comfortable to handle, then cut into pieces. Remove and discard the onion halves with their cloves.

3. Divide the pork among rimmed bowls, then ladle the soup over it. Pass a bowl of grainy brown mustard at the table.

Enjoy this wonderful Swedish tradition served hot with chunks of bread.