Prompted by a discussion at English.se I may be going to make Mrs Beeton's soda biscuits recipe:
SODA BISCUITS.
- INGREDIENTS.—1 lb. of flour, 1/2 lb. of pounded loaf sugar, 1/4 lb. of fresh butter, 2 eggs, 1 small teaspoonful of carbonate of soda.
Mode.—Put the flour (which should be perfectly dry) into a basin; rub in the butter, add the sugar, and mix these ingredients well together. Whisk the eggs, stir them into the mixture, and beat it well, until everything is well incorporated. Quickly stir in the soda, roll the paste out until it is about 1/2 inch thick, cut it into small round cakes with a tin cutter, and bake them from 12 to 18 minutes in rather a brisk oven. After the soda is added, great expedition is necessary in rolling and cutting out the paste, and in putting the biscuits immediately into the oven, or they will be heavy.
Time.—12 to 18 minutes. Average cost, 1s.
Sufficient to make about 3 dozen cakes. Seasonable at any time.
[italics mine]
Does she really use sodium carbonate and not sodium bicarbonate? I know I can bake the latter to make the former but the carbonate is reputed to leave a soapy flavour. Can we tell from the need for haste after adding it (a quicker reaction?) Does the era give us a clue (mid-C19th)?