This is a typical regional recipe from the middle of the province of Noord-Holland, the Zaanstreek in the Netherlands. The Zaanstreek is situated right above Amsterdam; tourists mostly know it for the mills and old wooden houses at the Zaanse Schans. Here you can find the mill that was the first to make the Zaanse Mosterd (Zaanse mustard). This mustard is coarse and have whole yellow and brown mustard seeds. This is the only kind of mustard you can use for this recipe! When the soup is warm, serve with freshly baked and buttered bread. Eet smakelijk! Good appetite!