horn and hardart sold this food baked in individual casseroles in
their "automat cafeterias" in manhattan during the 1930s to the 1960s

I've found five slightly different recipes for you to try. The
original recipes have been kept secret, but I recommend the last of
these as the most authentic re-creation of Horn and Hardart's mac &
cheese casserole.

Recipe Link: Horn and Hardart Baked Macaroni and Cheese
http://www.recipelink.com/ch/2002/december/theautomat2.html

The Food Maven: Horn & Hardart's Macaroni and Cheese
http://www.thefoodmaven.com/radiorecipes/mac_cheese.html

The Automat: Horn & Hardart's Macaroni and Cheese
http://www.theautomat.com/inside/recipes/mc.html

Online Cookbook: Horn & Hardart's Macaroni and Cheese 
http://www.online-cookbook.com/goto/cook/rpage/000E62

Uncle Phaedrus, Finder of Lost Recipes
http://www.hungrybrowser.com/phaedrus/m050203.htm#3

Google Web Search: automat "macaroni and cheese"
://www.google.com/search?hl=en&q=automat+%22macaroni+and+cheese

I hope this is precisely what you need. If anything is unclear or
incomplete, please request clarification; I'll be glad to offer
further assistance before you rate my answer.

Best regards,
pinkfreud