A recipe for “toast sandwiches,” from Mrs. Beeton’s Dictionary of Every-Day Cookery, 1865:

Ingredients. — Thin cold toast, thin slices of bread-and-butter, pepper and salt to taste. Mode. — Place a very thin piece of cold toast between 2 slices of thin bread-and-butter in the form of a sandwich, adding a seasoning of pepper and salt. This sandwich may be varied by adding a little pulled meat, or very fine slices of cold meat, to the toast, and in any of these forms will be found very tempting to the appetite of an invalid.

In 2011 the Royal Society of Chemistry worked out the nutritional content:

3 slices of white bread = 240 Calories. Butter = 10 g = 90 Calories
Total = 330 Calories
Toast sandwich nutrients
Protein = 9.5 g
Fat = 12 g
Carbohydrate = 55 g
Fibre = 4.5 grams
Calcium = 120 mg
Iron = 2 mg
Vitamin A = 90 mcg
Vitamin B1 = 0.25 mg
Vitamin B2 = 80 mcg
Vitamin B3 = 4 mg
Vitamin D = 0.08 mcg

“I’ve tried it and it’s surprisingly nice to eat and quite filling,” said he RSC’s John Emsley. “I would emphasise that toast sandwiches are also good at saving you calories as well as money, provided you only have one toast sandwich for lunch and nothing else.”