Ammonia Cookies(German Christmas Cookies)

Dissolve baker's ammonia in a spoonful of milk so it distributes evenly through the dough.

Cream butter and sugar, then beat in eggs, vanilla, lemon zest, and the ammonia mixture.

Mix in flour to form a firm dough, wrap it, and chill until easy to roll.

Roll thin, cut into Christmas shapes, and sprinkle with coarse sugar.

Bake until set and barely golden, then cool fully so the cookies become crisp.