Start by preheating your oven to 180°C (350°F), greasing a 2-lb loaf pan with butter, and dusting it with a bit of flour. Set loaf pan aside.
Use a strainer to sift flour and baking powder into a medium bowl.
Add the poppy seeds, then mix.
Using a large mixing bowl, combine butter with sugar, then mix until it’s creamy.
Add the yolk, honey, lemon zest, and milk, then continue mixing to combine evenly.
Add the dry ingredients from earlier --- flour, baking powder, and poppy seeds.
Mix until just combined, then set batter aside.
Beat the egg whites until you get stiff peaks.
Add 1/3 of the beaten egg whites into the batter and fold gently to combine.
Add the remaining egg whites in batches; do not overmix, but just enough to combine the whites with the rest.
Pour the batter into the greased loaf pan.
Tap the pan gently on the counter to get rid of bubbles.
Place the pan in the lower part of the oven for 35 to 40 minutes; or until a toothpick comes out dry when you stick it in the cake.
Take your poppy seed loaf out of the oven and set it aside to cool.
Prepare the icing by combining the powdered sugar with the lemon juice and mix until you get a thin texture.
Pour the lemon icing on the cooled cake.
Your lemon poppy seed loaf is now ready for slicing and serving --- enjoy!