Is chocolate cake a common or a proper noun?

The compound noun 'chocolate cake' is a common noun, a Word for any chocolate cake of any kind.

A proper noun is the name of a specific person, place, thing, or a title; for example;

• Chocolate Cake Communication Design, Lincoln, NE
• Chocolate City Cake & Pastries, Union City, NJ
• Strip House 24-Layer Chocolate Cake, available at Nieman Marcus ($115.00 +S&H)
• Pepperidge Farm Chocolate Fudge 3-Layer Cake
• "Chocolate Cake With Hitler" by Emma Craigie