Wash the mugwort thoroughly and drain off the water.
Add eggs and sugar to a bowl and whisk well until foamy.
Sift in the cake flour, baking powder, and salt, then mix until just combined.
Add milk, melted butter, and mugwort to the batter and mix until smooth.
Pour the batter into a cake pan and bake in a preheated oven at 170°C (338°F) for 30 minutes.
Remove the cake from the pan and let it cool completely on a wire rack.