Mosterdsoep is a traditional soup made with a combination of flour, butter, stock, cream, leeks, and coarse grain mustard (preferably Groningse or Zaanse mosterd). This soup is a specialty of Groningen. If desired, bacon and white wine can be added to the soup for extra flavor.

Once cooked, the soup is traditionally ladled into bowls or soup plates and garnished with chopped chives or bacon bits. This velvety, creamy soup is especially popular during the winter.