Remove the seeds, cut half of the kabocha squash (about 100g) into cubes, place into a microwave-safe bowl, cover with plastic wrap, and microwave. Cook at 500W for 1.5-2 minutes.
Cut the remaining half into 3cm pieces, and microwave just like the kabocha from Step 1. Microwave at 500W for 4 minutes. They are done once you can pierce them through with a toothpick. Remove the rind, and mash into a paste. Tip: It is hot, so be careful.
Line a pan with parchment paper (You can also use copy machine paper.) Preheat the oven to 340F/170C.
Once the kabocha has cooled, add the butter and salt to a bowl and whisk with an egg beater until smooth. Add in the sugar in 3 batches.
After completely mixing in the sugar, whip the mixture until it turns completely white. Add in the mashed kabocha and mix.
Whisk the eggs and add the vanilla oil. Add the eggs, one tablespoonful at a time, to the mixture from step 5, mixing well. Tip: Add in the next spoonful of egg after mixing well enough that the mixture looks like it did before the previous egg was added.
Sift the flour and baking powder into the bowl. Mix it together with a rubber spatula, using short, light strokes as if you're cutting the mixture. Stop after you are no longer able to see the flour.
Add the kabocha squash from Step 1 that was cut into cubes. Gently fold it in so as not to smash the kabocha. Make sure not to over-mix.
Pour it into the pan. Top with kabocha squash seeds to taste.
Bake in an oven preheated to 170C for 45-50 minutes. After cooking for 15 minutes, make a cut down the center of the loaf.
Once it has all plumped up and the opening in the middle springs back up when lightly pressed on, it is done.
Story Behind this Recipe
I was pondering what to make for Halloween this year... I wanted to eat something sweet that had the pretty color of kabocha squash, so I thought this up.
When adding in the kabocha squash, it's important to not let the butter and eggs separate! Please whip thoroughly in step 4. It separates easily if you use eggs taken straight out of the fridge. You can make this in the exact same way using sweet potatoes.