Scald milk in a small saucepan

Put the ammonium carbonate in small bowl, pour the hot milk over it, and cover bowl with a plate or lid as the mixture foams up

Let this mixture cool while oiling two large baking sheets

Blend shortening and sugar in a large mixing bowl

Beat into this the eggs, lemon extract, remaining 1/2 cup milk, and 2 cups of flour

Stir in the cooled milk mixture (no longer foamy) and another cup of flour to make a stiff batter

Add more flour, 2 cups at a time, until the dough is firm enough to roll out. Turn out onto a lightly floured surface and roll dough into a rectangle about 10 inches by 23 inches by 1/4 inch

With a floured knife, cut the dough into 2-1/2 inch squares, about 36 in all. Preheat the oven to 350F

Place squares on the bak- ing sheets so they are not touching and prick them with a fork to make a design

Bake crackers in a moderate oven until they are lightly tanned, 10 to 15 minutes

Remove from pans to cool

Makes about 3 dozen crack- ers.