Use a strainer to sift flour and baking powder in a medium bowl.
Add 4 tablespoons of 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 cake 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 into the rest.
Pour the batter into the greased cake 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 cake out of the oven and set it aside to cool.