Spanish omelette vs frittata

Spanish omelette

noun
  • A molded omelette made with the addition of fried potatoes and often onions. 

frittata

noun
  • A crustless quiche: a molded omelette in which vegetables, cheese, etc., are mixed into the eggs and cooked together. 

How often have the words Spanish omelette and frittata occurred in a corpus of books? (source: Google Ngram Viewer )