Steam the kabocha squash, remove the skin, and mash it well.
Cream the butter and sugar together until smooth.
Add the eggs one at a time, mixing well after each addition.
Add the mashed kabocha squash and mix.
Sift in cake flour, baking powder, and salt, then combine gently.
Pour the batter into a pound cake mold and bake in a preheated oven at 170°C (338°F) for 40 minutes.