In the days before baking powder and baking soda, people relied on an old-fashioned leavening agent called baking ammonium to give an extra oomph to their cakes and biscuits. Though more familiar in the kitchens of our grandmothers and great-grandmothers, it is still used in old-fashioned recipes like gingerbread and springerle to create extra crisp biscuits with a light and airy texture. There is nothing like it.
Baking ammonium is the star ingredient in the aptly named Ammoniaczki, or ammonia cookies. The original recipe came folded inside a letter my Babcia sent from Poland years ago, and having never encountered anything like it (cookie or ingredient) I was intrigued. The slightly morbid name is well suited; a sniff of baking ammonium will burn the hairs in your nostrils and a strong scent will seep as the biscuits puff up in the hot oven. Thankfully this dissipates by the time the biscuits are done and have cooled on a wire rack. Novelty factor aside, make these, they are one of a kind.
*NOTE. It is worth sourcing a small jar of baking ammonium, even as an emergency aid for fainting spells. Try the baking aisle of the supermarket but I have found continental stores and baking specialty stores the best bet. Although I haven’t tested this myself (disclaimer!) I have heard you can substitute 1:1:1 baking ammonium with equal parts baking powder and baking soda, combined.
Whisk together the flour and baking ammonia in a large bowl then whisk in the sugar. Add the butter in small lumps, half the beaten egg, the sour cream and vanilla extract. Rub the mixture together with your fingertips until large coarse crumbs form. Keep rubbing until they start to lump together into a ball, becoming more damp than floury, gathering the remainder as you go. It will be sticky and streaky; this is fine. Wrap this lump with cling film and leave aside for at least 10 minutes, but up to 30 minutes will be okay.
Arrange the racks in the oven to accommodate two trays (if necessary, otherwise just keep one rack in the middle) and preheat the oven to 200°C (180°C fan-forced/ 400°F). Grease and line two large baking trays.
Unwrap and shape the dough into a rounded, but flat log, as you would with biscotti. Not too wide. Roll it out with your hands if you find it easier. Cut even ‘slices’ of dough, just under a centimetre thick, and place each one on a baking tray leaving a 2-3cm gap between them.
Tip the sugar into a shallow bowl. Brush the tops and sides of the biscuits with the remaining egg. Take a biscuit and press into the sugar, coating the top and side. Re-arrange back on the tray and continue for the remaining biscuits.
When the oven is hot enough (mine has a light that switches off at the indicated temperature), insert the trays and bake the biscuits for 10 minutes but check after 8 minutes, or until very lightly golden in colour. You may be able to smell faint whiffs of ammonium (this is fine) and the biscuits will expand dramatically. Remove from the oven and let them cool on a wire rack. Turn them over to check if the bases are light golden and firm to touch. These biscuits are inedible under-baked (the smell will linger), but over baked will make them tasteless. Trust your instincts!