“Thumbers” are thick beef, pork, or mutton sandwiches that were popular crowd food at the Newmarket racetrack. The name alludes to the small-sized sandwiches held between the thumb and forefinger. Except for gastronome Edward Spencer. in his Cakes & Ale: A Memory of Many Meals and a recipe for “Thumbers,” dignified with the name Bookmaker’s Sandwiches in Escoffier’s The Complete Guide to the Modern Art of Cookery, these sandwiches are unknown in literature and cookery.

2337— Bookmaker Sandwiches. In his book, “La Cuisine Anglaise,” Mr.] Alfred] Suzanne gives the following kind of sandwich, which deserves attention: —This kind of sandwich, which is liked by racing people, is a most substantial affair, and it will be seen from the following recipe that a sandwich of the nature prescribed might, in an emergency, answer the purpose of a meal. Take an English tin-loaf, and cut off its two end crusts, leaving on them about one-third inch of crumb. Butter these crusts. Meanwhile, grill a thick steak, well-seasoned with salt and pepper. When it is cooked, cool it; sprinkle it with grated horseradish and mustard, and lay it between the two crusts. String the whole together as for a galantine, and wrap it in several sheets of blotting paper. Then place the parcel under a letterpress, the screw of which should be gradually tightened, and leave the sandwich thus for one-half hour.   At the end of this time, the insides of the slices of bread have, owing to the pressure, become saturated with meat juice, which is prevented from escaping by the covering of crust. Remove the blotting paper, and pack the sandwich in a box or in several sheets of white paper.  

See Edward Spencer. Cakes & Ale: A Memory of Many Meals, the Whole Interspersed with Various Recipes, More or Less Original, and Anecdotes, Mainly Veracious. G. Richards, 1897; August Escoffier’s The Complete Guide to the Modern Art of Cookery (Paris, 1903). Trans. James B. Herndon London, Heinemann,1907