In a large bowl, cream together the butter and brown sugar until light and fluffy. Beat in the egg, then stir in the vanilla and lemon zest. Combine the flour, baking powder and spices; stir into the sugar mixture and blend thoroughly until fully incorporated. Scrape onto a lightly, floured board and knead a few times, just until the dough is smooth and pliable.
Turn onto a sheet of plastic wrap and roll into a log, wrap up and refrigerate for several hours or freeze for 2 hours.
Line baking sheets with parchment. Cut the dough into about 1/8" thick slices and place them on the sheets about an inch apart (they won't spread very much, but they need air and space around each cookie). Bake until the edges just begin to turn golden, about 16-18 minutes. Remove and let cool before serving.