In a medium bowl, sift together flour, baking powder and salt. In a large bowl, beat the butter and lemon zest on medium speed, until light and smooth. Add sugar, eggs, coriander and mace; beat until smooth. Add half the milk and beat just until blended (the batter will look curdled). Reduce the speed to low, add the flour mixture in 2 batches, beating just until blended and scraping the bowl as needed. Add the remaining milk and mix just until blended. Stir in caraway seed. Scrape the batter into prepared loaf pan; smooth the top.