Preheat the oven to 350°F (175°C). Grease and flour a 9x5-inch loaf pan.
In a medium bowl, whisk together the flour, baking powder, and salt.
In a large bowl, cream the softened butter and granulated sugar until light and fluffy, about 3-5 minutes.
Add the eggs, one at a time, mixing well after each addition. Stir in the lemon zest and juice.
Gradually add the dry ingredients to the wet mixture, alternating with the milk, starting and ending with the flour mixture.
Gently fold in the poppy seeds until evenly distributed.
Pour the batter into the prepared loaf pan, smoothing the top with a spatula.
Bake for 50-60 minutes, or until a toothpick inserted in the center comes out clean.
Let the cake cool in the pan for about 10 minutes, then remove it and transfer to a wire rack to cool completely.
Once cool, dust with powdered sugar if desired and serve.