Sift flour and baking ammonia together and crumble the butter into it. Mix in the remaining ingredients and knead well. Divide the dough into 3 and roll them into sausages, placing them on a baking sheet with parchment paper. Flatten the sausages with your palm and bake in a preheated oven at 180 degrees Celsius (356 degrees Fahrenheit) fan-forced for 10 minutes. Mix powdered sugar, rum essence, and water in a bowl. While the slices are still warm, spread the glaze on and cut them into appropriate pieces. Let them cool on the baking sheet.