Just as every year, I have been baking spicy Christmas cookies with my Granny. And like always, they have expanded nicely in the oven, but collapsed afterwards. But this year I know to go to Seasoned Advice and ask how to prevent that for years to come!
The recipe calls for 625 g sugar, 250 g butter and 50 g various dry spices (cinnamon, coriander, succade, cloves) to be kneaded together, and then to be mixed with 875 g flour and 250 ml milk with 15 g baker's ammonia (Ammonium carbonate). The dough is laid to rest for a long time (4 days or so), rolled about 3mm thin, cut, and baked at 160⁰C for 10–12 minutes.
The cookies expand in the oven, growing a bit thicker in the middle than on the outside, but then collapse again during the remainder of the baking time. The resulting cookies are quite soft when coming out of the oven, but grow very hard during cooling.
What would we need to change so that the cookies keep their expanded shape?