Yudane (Skip to next section if not using yudane)

1. In a small bowl, combine 60 g of bread flour with 60 g of boiling water. Mix until it forms a dough.
2. Wrap it in plastic wrap or place it in an airtight container and let it sit at room temperature for at least 4 hours or overnight in the fridge.

Main Dough

1. Prepare the Kabocha: Peel and cut the raw kabocha into small cubes. Place it into a bowl, cover and microwave the kabocha until soft, about 1-2 minutes. Weigh the kabocha, it should be about 45 grams. If it’s more, reduce the amount of milk (90 ml). If less, use more milk (100 ml). Mash the cooked kabocha until smooth, and let it cool to room temperature.
2. Make the main dough: In a mixing bowl, combine the milk, egg, sugar, mashed kabocha, bread flour, yeast, and salt. Mix until the dough comes together. Knead in the yudane until well incorporated. (If you’re not using yudane, add the extra bread flour and water that would have been in the yudane directly to the main dough). Then, knead in the butter until fully absorbed. The dough will be sticky at first, but continue kneading until it becomes smooth and elastic—about 10-15 minutes by hand or 7-10 minutes using a stand mixer. The dough should be soft but not too sticky to the touch.
3. First proof: Place the dough in a bowl or container, cover and refrigerate overnight in the produce compartment. If using the same day method, cover the dough with a damp cloth and let it rise in a warm place for about 1-1.5 hours, or until doubled in size. In the meantime, prepare custard cream if using.
4. Shape: Remove from fridge and let it sit out for 60-90 minutes or until the dough is about 18°C to 20°C / 64.4°F to 68°F .  Punch down the dough and divide into equal portions (about 50 grams each). Shape each portion into a round ball. Place them on a piece of parchment paper.
5. Second rise: Cover and let them rise for 30-45 minutes or until puffy and double in size. 
6. Deep fry: Heat oil in a deep pot to 210°C to 220°C (410°F to 430°F), aiming for the lower end. Fry the donuts 2-4 pieces at a time (depending on pot size) for 60 – 70 seconds per side until deep brown. They will be darker than your traditional donut. 
7. Coat donuts: Remove the donuts and drain on a wire rack or paper towels. Make the glaze by stirring the powder sugar and liquids. Start with lesser amount and adjust consistency. The runnier the glaze the thinner it will be on the donut. Add powdered sugar or sugar to a shallow bowl if using these as the coatings. While still warm, coat in powdered sugar, granulated sugar or a glaze as desired. If filling with cream, wait until they are completely cool. 

Filling

1. Prepare the Piping Bag: Take a piping bag and fit it with a round tip.
2. For whip cream: Add sugar to the heavy cream and whip until stiff peaks. 
3. Fill the Bag: Carefully spoon the diplomat cream or whipped cream into the piping bag. You can also place the piping bag inside a tall glass or jar to help keep it open while you fill it. Once filled, squeeze out any air, and seal the top.
4. Pipe the Cream: Take a chopstick and insert it into the side of a donut while wiggling it to make room for the cream. Insert the piping tip into the side of the donut and gently squeeze the bag to fill the donut with diplomat cream (about 45 grams each). Move the piping bag in and out slightly while squeezing to ensure even filling.
5. Finish: Once filled, remove the piping tip and repeat with the remaining donuts.