1 Dissolve potash in 3 tablespoons warm water. Rinse lemon in hot water, wipe dry, finely grate the peel and place in a bowl.
2 Mix honey with tea in a pot. Mix in sugar, milk and goose fat, stirring constantly. Heat until warm while stirring. Remove from heat and transfer to a mixing bowl.
3 Mix together chopped almonds, whole wheat flour and grated lemon peel. Stir in vanilla sugar, cinnamon, clove, anise seed, cardamom, mace and cayenne pepper.
4 Mix ingredients well. Add potash and honey mixture and knead thoroughly with a hand mixer on low speed until dough is firm.
5 Pour mixture into a bowl, sprinkle dough with a little flour and cover with plastic wrap. Ideally, leave the bowl for at least 1 week standing at room temperature and for up to 6 weeks. By doing so, in a process similar to leavening bread, lactic acid bacteria will develop to loosen the dough and give it flavor (this is referred to as "fermentation").
6 Knead the finished fermented dough briefly then put into plastic wrap and sprinkle with a little flour. Cover with a second layer of plastic wrap.
7 Roll sheet out until about 5 mm (about 2 inches) thick. Cut gingerbread into 35 rectangles or diamonds. For Advent or the Christmas season, cut out seasonal shapes to taste or form walnut-sized balls.
8 Line a baking sheet with parchment paper. Distribute gingerbread on baking sheet about 4 cm (approximately 1 1/2 inches) apart and bake in preheated oven at 180°C (fan: 160°C, gas mark 2-3)(approximately 350°F/convection 325°F) for 8-12 minutes depending on thickness.
9 Remove gingerbread and let cool briefly on baking sheet. Then transfer to a wire rack and let cool completely.