Preheat Oven: Preheat your oven to 150°C (302°F).

Combine Wet Ingredients: In a mixing bowl, combine the egg, egg yolks, vegetable oil, and pumpkin puree. Mix until well combined.

Add Dry Ingredients: Sift the cake flour into the mixture and gently fold until fully incorporated.

Beat Egg Whites: In a separate bowl, beat the egg whites until they become foamy. Gradually add the sugar and continue beating until stiff peaks form.

Fold Ingredients: Gently fold the beaten egg whites into the pumpkin mixture in three additions, being careful not to deflate the batter.

Prepare Pan: Pour the batter into a cake pan lined with parchment paper.

Create Water Bath: Place the cake pan into a larger baking dish filled with hot water to create a water bath.

Bake: Bake at 150°C (302°F) for 80-100 minutes, or until a toothpick inserted into the center comes out clean.

Cool: Remove from the oven and let the cake cool in the pan for 10 minutes before transferring to a wire rack to cool completely.