Hemingway's favourite burger recipe

The treasures one can find sometimes reading the news, or looking into old stuff. I have learned on BBC News that they found out Ernest Hemingway's favourite burger recipe. With his own handwriting on it. It gives an interesting sight of Hemingway's mind and (especially) stomach. And I am curious about the recipe itself: it has capers in it and I love capers. A strange, but very tempting thing to add to a burger recipe. There are many things in it I have no idea what it is and wonder if I could find it anywhere: India relish, Spice Islands Beau Monde Seasoning, Spice Islands Mei Yen Powder, what have you. All the same, I'd love to try it, or something close to it. Just for kicks and because it is Hemingway's favourite burger recipe. Come to think of it, while I love burgers, I have no specific favourite recipe.