1. In a small bowl, combine the poppy seeds and milk. Let stand 1 hour to macerate and meld flavours.
2. Preheat oven to 325F. Cream the butter and sugar in the work bowl of an electric mixer. Add the eggs one at a time, beating well after each addition. Combine the flour, baking powder, lemon zest, and salt in a small bowl. Add the dry ingredients to the creamed mixture in three equal portions, alternating with the poppy seed milk. Beat just until smooth.
3. Pour the batter into a greased 9-by-5-inch loaf pan and bake in the centre of the preheated oven until golden brown and a cake tester inserted into the centre of the loaf comes out clean, about 55 to 65 minutes. Place the loaf in the pan on a cooling rack.
4. Meanwhile, to make the lemon syrup, combine the sugar and lemon juice in a small saucepan. Place over low heat just until the sugar dissolves. Set aside. Pierce the hot loaf about a dozen times to the bottom with a bamboo skewer, toothpick, or metal cake tester. Immediately pour over the hot lemon syrup. Cool 30 minutes before turning out of the pan onto a rack to cool completely. Wrap tightly in plastic wrap and let stand at room temperature overnight before serving.