Hemingway’s 4th wife Mary wrote that they ate the hamburgers to fortify them for “tramping through the sagebrush after pheasant, partridge or ducks” in Idaho or Wyoming, which they visited every autumn. She typed the recipe out for the Woman’s Day Encyclopedia of Cookery while Hemingway was still alive.The version above, with the  “Wild West” annotation, was for a later edition.
Ingredients included:

• 1 pound of lean ground beef
• two minced garlic cloves,
• 2 little green onions, finely chopped,
• India relish,
• capers,
• Spice Islands Beau Monde sages seasoning,
• Spice Islands Mei Yen powder,
• 1 egg beaten in a cup with a fork

The ingredients are readily available except for Mei Yen Seasoning. Luckly I found the following on a forum
“Mei Yen Seasoning Substitute
I contacted Spice Islands asking them if they could recommend a substitution for Mei Yen seasoning as several recipes in their cookbook require it and I could find it no where. They responded as follows:

Spice Islands Mei Yen has been discontinued, but you can make your own by combing: 9 parts salt, 9 parts sugar, 2 parts MSG ( Accent Flavor Enhancer)

Combine and store in tightly closed container. To use, if recipe calls for 1 tsp. Mei Yen: use 2/3 tsp. substitute recipe and either 1/8 tsp. bouillon powder or 1/8 tsp. soy sauce.”

You will notice that MSG is an ingredient of the Mei Yen seasoning.  MSG ( Accent Flavor Enhancer) was popular in the 1950’s Lucy era and a shaker of Accent Flavor Enhancer even appeared as a prop in Lucy’s kitchen. It fell out of favor due to a health scare,  but Monosodium glutamate has since been declared generally safe (Ref FDA 1995) and you can buy it on Amazon as Accent Flavor Enhancer