flapjack vs potato pancake

flapjack

noun
  • A pancake. 

  • A bar made of (though not limited to) rolled oats, butter, golden syrup, and brown sugar, baked in a tray. 

potato pancake

noun
  • A shallow-fried pancake of grated potato and egg, often flavored with grated onion 

How often have the words flapjack and potato pancake occurred in a corpus of books? (source: Google Ngram Viewer )