Where to classify works on cooking vegetarian soups? Browsing the Relative Index for "soups" yields:
Browsing the Relative Index for "Vegetarian cooking" yields:
Vegetarian cooking 641.5/636
In the upward hierarchy for 641.5636 Vegetarian cooking is 641.5 Cooking. In the record for 641.5 is the see reference: "For cooking specific kinds of dishes, preparing beverages, see 641.8." That see reference has hierarchical force; hence works about cooking vegetarian soups are classed in 641.813 Soups. Examples are Vegetarian Soups and 365 Vegetarian Soups. For these works, the first LCSH is "Soups," and the second is "Vegetarian cooking." For works like these, to provide additional access beyond that provided by the standard DDC number 641.813 in MARC field 082 - Dewey Decimal Classification Number, one could put the additional DDC number 641.5636 in the MARC field 083 - Additional Dewey Decimal Classification Number.
What about chicken soup? Browsing the Relative Index for "chicken" yields (among other things):
Chicken (Meat)—cooking 641.6/65
In the upward hierarchy for the built number 641.665 Poultry (Meat)—cooking is 641.6 Cooking specific materials. In the record for 641.6 is the class-elsewhere note: "Class specific kinds of dishes featuring specific materials in 641.8." That note also has hierarchical force. Hence cooking chicken soup is classed with cooking soup in 641.813 Soups. Examples are The Chicken Soup Book: Old and New Recipes from around the World and Chicken Soup: 38 International Recipes from Traditional to Contemporary. For these works, the first LCSH is "Soups," and the second is "Cooking (Chicken)." For works like these, to provide additional access, one could put the additional DDC number 641.665 in the MARC field 083.